I recommend looking into these 3 technical areas specifically for the sell side to buy side transition:
Expand Coverage: Sell side typically cover a narrower set of names of between 10-20, while research analysts on the buy side typically can look at 30-50 names. Perhaps you cover a sub-sector in healthcare service, medical equipment, or maybe just bio-tech. I recommend expanding your coverage universe by getting familiar with healthcare names that you are not researching every day.
Portfolio Management: On top of your modeling skills, if you know pivot tables and building models to analyze large data sets, that would be very helpful to a portfolio manager. Relative valuation is more important on the buy side, and if you can help your PM get through a large set of data to screen out names or pinpoint marco/industry trends, you would stand out among the pack.
Credit: You’d want to go to an equity shop, but if you know credit then it’d be even better. Equity hedge funds are happy to look at credit opportunities if it makes them money. If you can analyze high yield and identify credit opportunities in addition to equities, you would be valuable to the PM.