Find a nice target. Ideal characteristics are large caliber (idealy > 0.5mm), less than 1cm deep, and straight. For the last part you need to trace up and down a little bit once you’ve found your target to make sure it’s straight.
Once you’ve got your target, pierce the skin and find your tip right in the middle of your probe. Move probe toward needle and gently wiggle the needle to help find it. Once found, advance needle toward vein a few mm at a time. Slowly advance probe ahead of needle a few mm. Advance needle again so tip is in view. Continue this back and forth advancement until needle tip is tenting the vessel. Pierce through and visualize tip in vessel (looks like a little donut).
Most people that aren’t facile with US guided IVs will screw up here. They get flash and try to thread the catheter. DO NOT thread the catheter yet. Flatten out your angle (flat as you possibly can), still visualizing needle tip in vessel. Now advance probe 1-2 mm till needle tip is just out of view. Now advance needle til tip is in view again within the lumen. Now advance probe again 1-2mm til tip is out of view then advance needle again just til tip is visualized.
Continue this back and forth until at least .5-1cm catheter is in the lumen (sometimes I’ll walk half the catheter in if I have time if I’m not in a hurry), THEN thread off catheter.