What legal prep should I do for Series A?

1. Finalize cofounder equity.  Sometimes companies haven't issued stock to a cofounder yet. It may be too late to do tax-free. Post term sheet will definitely be too late to do tax-free. Finalize the issuance with your law firm asap.
2. Fix any missing 83(b) filings. Missed 83(b)s can sometimes be fixed pre-term sheet. Usually unfixable post-term sheet.
3. Finalize employee stock grants. You can often keep granting stock to employees pre Series A. But you'll have to switch to stock options post Series A. Not as valuable. 
4. Ex-cofounders. Resolve any conflicts with ex cofounders. Also former employees with equity or who had technical roles but didn't assign IP. Those people will have leverage over your financing and can tank your Series A.
5. Expand your board. If you don’t control 3 common board already, add those seats before Series A fundraising. 

Most other things can be addressed post-term sheet.