Two most important signals 1. On Partner's opening lead 2. When you or partner make your FIRST discard - When you don't follow suit for the first time. I recommend playing attitude on both of those discards. (Encourage or Discourage, so either low encourage or high encourage, whichever you and your partner prefer).
The most important signals
Try not to double with a 5 card major
Bid as high as possible!
Defending against a multi 2D
Always transfer with a 5 card major.