Mat Blumberg has a nice post on  how to negotiate a  term sheet with a VC.
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Here’s the summary:

1. Get a good lawyer.**

2. Focus on terms that matter, otherwise known as Pick your battles. A typical VC term sheet will have at least 20 terms spelled out in it. There are only a few that really matter in the end, although you should at least make sure your lawyer is comfortable that the others are reasonable and somewhat standard. Spend time on valuation, the type of security, the option pool, Board composition, and your own compensation and rights.

2a (new). Sacrifice valuation for a clean security. Everyone always thinks that price/valuation is the most important thing to maximize in a deal. However, the structure of the security can be much more important in the long run. Whether the VCs buy 33% of your company or 30% of your company is much less important than having a capital structure that’s easy for an outsider to understand and want to join (e.g., investment banker or later-stage VC).

3. Always have a BATNA

4. Be prepared to pay up for high quality investors. There is a world of difference between good VCs and bad VCs (both the individual partners and the firms) that will ultimately have a lot to do with how successful your company can become. The quality of your VC isn’t more important than the quality of your product or your team, but it’s right up there. But – and this is an important but – you should expect to “pay” for quality in the form of slightly weaker terms (whether valuation or type of security). This is where having a BATNA really comes in handy.

5. Ask for references.

6. Don’t let the VC get away with negotiating a point by saying “we always do it this way.”

7. If you have multiple investors in the syndicate, insist on a single investor counsel and a lead investor. This is essential to (a) protect your sanity, and (b) prevent you from paying zillions of dollars in legal fees. You have to make the VCs stick to it, though – they can’t come back and re-trade the deal after it’s been negotiated. This is also helpful in getting a syndicate cooperating with each other and aligning the members’ interests, particularly if it has investors who have participated in different rounds of the company’s financing. Do expect to play moderator constantly throughout the process, however, to ensure that it goes smoothly.

8. Try do deal in advance with follow-on financings. When an investor doesn’t participate in a follow-on financing, it creates a total nightmare for you. Other investors will want to punish their wayward colleague and can create massive collateral damage in the process to common shareholders and management. Just as VCs will insist on something called “pre-emptive rights” (the right to invest in future financings if they want), you and your lawyer should insist on some protection in the event that one of your investors abandons you when you are raising more capital.

9. Handle the term sheet negotiation carefully. Whether it’s an initial round or a follow-on round, how you handle yourself in this negotiation sets the tone for the next stage of your relationship with the VC. The financing is the line of demarcation between you and the VC courting each other, and the VC joining your board and effectively becoming your boss.

10. Finally don’t forget to say thank you at the end of the process. Whether you send a formal email, a handwritten note, or a token gift, be sure to thank your VCs after a financing. They’re putting their butt on the line for your company, they’re investing in YOU, and they’re making it possible for you to pursue your dream. That deserves a thoughtful thanks in my book.