Practice. Make a new mistake every time. I still discover new ways things can go wrong frequently. You must be comfortable when you're placing it or you're going to have a harder time with fine motor control.
Set up your own work area. Move the vent, move the monitoring equipment, move the patient to the top of the bed. Turn the bed diagonally in the room (keep head of bed roughly where it is, maybe 2-3 feet from the wall, move foot end of the bed 1-2 feet in either direction, whichever the vent and lines will let you). Make sure all the tubes attached to the patient are coming with them (Foley, chest tubes, heater, etc.) Remove the headboard, lower all the IV poles attached to the bed, move all the IV lines to the foot of the bed so when they want to give you a procedural sedation bolus they don't have to reach under the drapes.
US both sides of the neck (I'm assuming you're mostly doing IJs). Unless there's a compelling reason to avoid the right side, do the right side, it's usually bigger. Generally you'll know if they're a vasculopath or have a know stenosis or you're needing to save the right side for HD or a monitoring line. US lower on the neck, closer to the chest. It generally makes for an easier insertion site and tapes up cleaner.
Lower the bed to a comfortable working height. Assuming the patient's very top of the head is directly against the very top of the mattress that will be somewhere between around your belt line. Lower the patient down flatish to make sure they won't do anything dumb hemodynamically or agitation wise. I don't use Trendelenburg but if you or the person helping you insists on it, plan accordingly and note comfortable working height. If they're awake try not to cover the entire head, it freaks enough people out it can screw up your line attempts.
Make sure your tray is reasonably close to where you are working. This might not be possible for some lines and the person helping you (I assume someone's sterile since you're uncomfortable with lines) will need to give you things as you request them.
Open your tray. Set it up the same way each time, every time (until you're comfortable, then it matters less). If your kits don't come with saline, gauze, enough sterile whatever bring that each time. Figure out who's going to help you with the lidocaine and sleeve for the US probe and tying the back of your gown. Open up all the stuff you can open before you need to get sterile, then get sterile and finish the rest of the set-up. Bring extra 4x4s, one of whatever packs of sterile ones your institution stocks. Bring an extra chlorswap as well.
Follow whatever institutional protocol you have in terms of site sterilization (before or after, gloves change, etc.).
I like to flush all my ports and put whatever caps nursing requests onto my line before I do anything else. I leave the final caps on the proximal and medial ports and only leave the distal port open. Open up your sutures, put all your dressing materials, suture, chlorhexidine patch, etc. to one side of your sterile field so if you make a bloody mess before then at least those supplies will still be clean.
Drape the patient, cover your US. Do not use more than one rubber band. Make sure the US won't contaminate the majority of your sterile drape while also not sliding off the bed. Put a little bit of gel on the site, just enough to get it greasy. You do not want mounds of gel, it just makes your life more difficult later. Prepare your skin lidocaine needle and your deeper needle. This is generally better with two separate syringes, esp on awake people. They will appreciate the extra lidocaine.
Determine your insertion site. I generally find it easier to use a lower site on the neck, closer to the chest. I note proximity to the carotid artery but unless it's directly overlying your venous insertion site I don't really worry about it too much.
Make a skin wheel (PPD) and massage into the skin. Place that needle somewhere safe. Use the longer (19G?, depends on your kit) lidocaine needle under US guidance as a pretend insertion needle. Use the same roughly 30 degree angle as you'd be placing your insertion needle and use either transverse or longitudinal imaging with your US to numb up the tract with a couple mL of lidocaine. I do try to place this needle into the IJ and if you're low on the chest it's usually superficial enough that you can get in. After you've determined how deep you need to go at that angle on that patient you'll have a good idea of which way you should point your insertion needle, at what angle and how deep you need to go.
For virtually all lines I only leave a couple 4x4s and the wire on the patient. Everything else stays on the tray. For awake/delirious people I leave the wire in the tray within easy reach (unless having a helper assist with the insertion). Ensure the wire is moving smoothly in the holder and the J hook has been straightened with the plastic guard on the holder.
I always prep my own insertion needle. ALWAYS. I leave just barely enough friction on the slip tip so there's no air leak but when the needle is in, all you have to do is gently grasp the hub of the needle and you can then pull off the syringe with a minimal amount of pressure.
Put the insertion needle through the skin at the same angle and trajectory as your deep lidocaine needle. Sometimes you need to give it a gentle push to get through tougher skin. If it's really tough grab the needle close to the tip (before you insert it) and then persuade it into the skin. This way you won't accidentally put a few more centimeters of needle into the neck when it goes through.
Learn to aspirate with your insertion hand as you'll be holding gentle pressure on the plunger as you go deeper. Make sure your own shoulders and neck are relaxed when you do this (hence position the patient at your belt line). Follow the path of your needle on either the transverse or longitudinal US view as it reaches and passes into the IJ. Once you get a flow of venous blood I suggest advancing another 1 mm just to make sure the wire doesn't get caught on the vessel wall.
After you've determined that you're in the IJ put the US probe down (style points lost if the cable then drags the US probe off the sterile field smashing the very expensive probehead on the ground) and use that hand to grasp the hub of the needle between your index finger and thumb. Use the other 3 fingers to stabilize against the neck (do not do a carotid massage). Aspirate with your insertion hand. This step is key. Every time there's a transition in your hands or body, aspirate to make sure you didn't jiggle the needle tip out of the vein. If you have, revert to the prior step.
If you're still getting good flow, ensure that you have your wire within reach. Pull syringe off needle with your insertion hand while holding the hub of the needle gently in place with the hand that was holding the US. You should see venous blood flow. If you see a pumper just put the syringe back on, gently remove needle and gently apply pressure to the carotid puncture. Wait several minutes and try again. Multiple carotid punctures generally ruin the site, you only really get 2-3 good attempts before you need to convert to another site.
Place syringe filled with venous blood on the field or tray. Take your wire and gently place into the insertion needle. Do not touch plastic to plastic, you will shove the needle through the back wall of the vessel and make yourself very sad. Smoothly advance the wire into the needle, avoiding touching the plastic of the wire holder to the plastic of the needle hub. This is very important, especially for smaller IJs that don't have much of a margin for error.
You should be able to easily advance 20-30cm into the vessel. This is very important for troubleshooting. If you meet resistance you must note where your start to meet it. If you're meeting resistance with ~8cm of wire your needle is no longer in the vessel. Roll the wire back into the holder, put it down, replace the syringe on the needle and attempt to move it back and forth 1-2mm and see if you can re-establish flow. This may require a new syringe if you got a lot of blood and it's clotted by now.
If you meet resistance beyond 10cm and are unable to advance the wire further I would suggest you pull back, ensure the J hook is pointed in another direction and attempt again. If you're getting resistance anywhere before 20cm I would not suggest using that site unless absolutely necessary as there's probably some type of significant stenosis. At that point you're done with this site (likely this side as I wouldn't generally recommend the SCV in this scenario either) and will need to plan your next move.
Assuming your wire is now somewhere around 20-25cm in, you can remove the insertion needle and put it somewhere safe in the tray. Don't worry about maintaining a death grip on the wire. It's not going anywhere. Do not coil the wire but make sure the end isn't flopping onto a non-sterile part of the bed. Take your scalpel and stab (no cutting, just tab) a bit deeper than 1cm. You'll need to experiment with this and adjust a bit depending on the size of the patient. Eventually you'll get a feel for how good this was by the resistance the dilator gives as you're placing it. Put the scalpel somewhere safe on the tray.
Take your dilator, thread over the wire and dilate about 3-5cm (again depending on the patient and how close your vessel was on US). After the dilator is deep "enough" grab your central line and place it within reach on the chest. The next step will cause some bleeding and the sooner the line is in, the less clean-up before you dress the site. Remove the dilator in one smooth motion, place on the chest and take your central line and thread it onto the wire until you can pinch the wire at the distal port. Insert central line to 15cm (or whatever your patient's size or site dictates). Be sure you have the cap for the distal port handy. I find it easier to just attach it to a saline syringe to ensure I don't lose it, plus it's one less step.
Flush, dress, clean-up, etc.
Repetition is the key. If you're new to line placements you should be spending as much time prepping the room and patient while not sterile as you plan to spend sterilely placing the line. I can generally tell how the line is going to go by how much trouble I have getting the patient positioned and visualizing the site before I even open up anything.
