1. Ensure that you have the latest of every one else's changes.
2. Build and compile everything.
3. Run ALL testcases.
4. Should any testcase fail - take care of it BEFORE commiting.
5. Make sure to check in ALL files necessary, including .csproj, data files, and testcases. Do a "show all differences" to make sure you're not missing any changed or added files.
6. Do not be afraid to ask someone to retrieve your changes to verify that they are ok.
I wrote these rules on a recent project I was on. These are the basic steps, there are more that have been said better by others before me, such as "Commit early, Commit often", and "Do not commit and run", and tools such as Cruise control to make your life easier.