These aren't hard fast rules but more of a way to consider your time. You may want to include things or not do certain things. Also, percentages will change based on your daily/weekly goals, or simply changing things.
1. Main money maker - 80%. That's my goal. That means 80% of the time I'm turking I'm doing something that is my main money maker. I know the requesters, I know what is expected, I know how much I'm making and I hope I'm focusing my efforts to turking and not not getting side tracked reading wikipedia or something. During this time I might think about keyboard shortcuts or other methods to complete the hits faster. In the short run I might lose some of my hourly wages, but I'm still looking at long term. If I think of something today to improve my productivity I might be able to earn more tomorrow or next week, etc.
2. Researching new requesters - 15%. Again, my goal. I'm happy with the requesters I do work for, however, sometimes I find new requesters. I might research them on TO or forums, or simply looking at hits available and seeing which ones I think I could make decent enough money on to do them. This doesn't mean I find a new requester a day. It may take a couple weeks or longer, and even then, it might just be a certain hit offered by the requester I think I could do. These hits I'm not as concerned about hourly wages, though it's still important. The theory simply is I can't find new requesters or hits if I don't take chances. I've found several quality requesters this way by doing hits that didn't seem to pay at first but after doing a handful of them I realized they are well worth it.
3. Improving stats - 5%. My personal final goal. Problem is, I'm happy with my stats. The only stats I'm not happy with is my abandoned and returned rate. But I can't improve these stats much since most of the hits I do is majority rules.
I can get 350 rejections without an approval to stay above 99%. Amazon mTurk doesn't go by tenths so only reason to try to get higher than 99.3% is to have a bigger cushion. A bigger cushion allows me to do more test hits for new requesters without worrying about my stats hurting. My submitted rate is 86.32%, which I'm not happy with. It doesn't prevent me from doing work, but I'd like to see that number go higher. Problem is, since I do mostly majority rules hits I return any hits I'm not sure about. I'd rather this stat not be great rather than not give the requester my best work I can do.