It will take more than a high step 2 ck obviously, but I would shoot for 250+ with 260+ pretty solidly demonstrating your ability to perform well on an exam.
With a low Step 1, you will need to make sure the rest of your application is pretty stellar if you want to aim for very competitive fields/programs. That means research, preferably good research with solid pubs to show for it. It means strong letters of recommendation, letters that glow so much you could use them for emergency lighting. Strive to honor all of your MS3 clerkships.
The truth is that most top students with 250+ on their step 1 will also be doing all of this stuff, so it's still an uphill battle. The end goal is to have your 220 be the ONLY thing on your application that anyone can say anything bad about. I've seen people match to good programs in competitive fields with an isolated ding like that, but they invariably had an otherwise flawless application. You need to start today (well, it's sunday - start tomorrow morning) with networking in your department of choice, getting involved with research, and being the rockstar you want people to think you are.
This time next weekend you should be doing one of the following: 1) finishing a rough draft of your protocol for IRB submission, 2) data collection/analysis, or 3)finishing the rough draft of a manuscript. Depending on what projects you find, aim to grab one by the horns and start getting something done asap. If something needs to be done in 2 weeks, turn it around in 2 days. There are few things that faculty at academic centers like more than a motivated med student who can get s--t done fast. This is what leads to glowing letters and great relationships.
Oh, and make sure you're working/studying hard enough to honor everything from here on out.
This will entail an insane amount of work on your part -- work that, based on your step 1 score, you have hitherto been unwilling or unable to do. Now's the time to change that.
