Just wondering what tips or tricks you guys might have to share. As always with posts like this, please only one tip per post so they can be voted on independently.
I'll start: however you do your theming, you can use the mothership theme as a base theme for your theme to inherit from so that your markup will be a lot cleaner and less verbose.
Two pieces of advice:
Don't blindly use the first module that shares a name with what you want it to do. Often the first module "captures" the namespace for that feature, but another, less aptly named module will fulfill the functionality better.
Look around for a way to do what you want that includes CCK/Views integration. This is pretty apparently the future of Drupal, so a standalone module that does what you want it to do that competes with a views/CCK-dependent module will probably die out in the near future.
++ to Geshan's suggestion.
