I am trying to learn this one myself. I know that when I am in the depths of depression, there is nothing anyone can do or say to make me feel better or re-enforce a positive attitude. I do remind myself that everyone gets depressed whether BP or not. People are just not always happy, it's a fact of life. Sometimes that makes me feel a little better knowing i'm not the only one and "normal" people can feel the same way. I do know that my depression tends to be so much worse than just being depressed. I literally cannot function properly and am always suicidal. I always repeat wonderful things about myself throughout the day but it just doesn't seem to make a difference. Medication, not shutting myself off from the world (I am notorious for that), music and reading helps me get through the tough times. The main thing is just knowing i'm not alone and everyone has bad times makes it a little more bearable.
Once medications is adjusted of course talk therapy and sometimes cognitive behavioral therapy are good as well. But as for practical ideas I'd say during depressive episodes the best thing to do is to find something constructive to do that will motivate you. Anything constructive that occupies your time even a hobby will do. Trying to find a way to be around people is essential as well. During mania obviously things are more complex but it is important not to have anything around that could be worsened by mania. Sometimes going online might not be a good idea. And for both states a good idea is to find emotional trigger points and "defuse" them and find accomodations around them. Ask yourself why they make you emotional and what they set off and if the process could be stopped beforehand. I've worked with this myself and helped other people with bipolar come to terms with it as well.