In recent meeting I discovered some sort of panic and anxiety when it comes to the first term sheet. You can go to YCombinator and others to download their term sheet. Startup Company Lawyer has many tips and links for the first term sheets at Startup Company Lawyer. Most notably, a posting from March 2010 dives into some details of seed and Series A investment documents http://www.startupcompanylawyer.com/2010/03/14/how-do-the-sample-series-seed-financing-documents-differ-from-typical-series-a-financing-documents/.
Chris Dixon also had good advice on first round terms back in August 2009 http://cdixon.org/2009/08/16/ideal-first-round-funding-terms.
A word of caution: a term sheet is really just an agreement on the terms “on a very high level”. Because the term sheet is only the basis for any legal documents, and only these are binding. But sometimes terms are not easy to put into legal text, especially if you happen to have some existing agreements or legal agreements. I recommend asking you lawyer or advisor a lot of questions to understand where in the legal documents you will find which terms; why the wording sounds so complicated; and what are risks and loop holes of the legal text at hand?
Another word of caution: Any legal document you got signed that talks about certain arrangements for the next round are vapor ware – if you cannot act out of a position of strength. The new investor might simply say “I want that changed” or “I want that taken care of before I lead your next round” – or otherwise the investor walks away. Do not think just because you have a signature on a piece of paper means that the deal is going to go down that way.