No need to worry guys... My approval rate was 72% after two months of turking...lol.... Now its 97.9, and hopefully will be 98 in a few days. All these took pace in just a few months. This is how we learn... I used to do a bunch of 0.00$ HITs everyday. around 30. Not to say, the HITs were extremely easy ones, and got approved in a flash. 20*30=600 approved HITs, without a single rejection... That tells the srtory!
I have been fortunate not to get rejected so far, (I am at 100%), but I have chosen carefully the hits I do, and I also had found the mturk forum when I began turking. That REALLY helped me alot.
90% isn't TERRIBLE, but you definitely want it to be higher than that. Many of the best HITs require 98%. I would suggest doing Catalog Choice and Redwood hits when they pop up. Quick simple penny hits, and have never had a rejection in hundreds of submits.
I just crossed 1100 accepted HITs, 400 are pending... sitting at 97%. Hoping to lock it in above 95% in these next few weeks so I can take a run of rejection