There are a few things you need to be on the lookout for when solving DS.
1. You need to know the quant. You can't ace DS questions if you do not know the basic concepts behind the question. You say you're doing pretty well in PS, so this might not be an issue for you. However, that's not true for everyone and I guarantee that almost all test takers can use a math refresher.
2. You need to first look at each statement separately. This is pretty easy for statement 1, but it's not so easy for statement 2. I know most people who have a tough time with DS actually forget that they need to completely ignore the info in statement 1 when they analyze statement 2. You might want to check to see if you are making that mistake. Here are the steps in solving DS:
Check 1.
a. 1 is sufficient --> check B
a1. 2 is sufficient --> answer is D. STOP.
a2. 2 is not sufficient --> answer is A. STOP.
b. 1 is not sufficient --> check B
b1. 2 is sufficient --> answer is B. STOP.
b2. 2 is insufficient --> check 1 and 2 together --> either pick C (if they are sufficient) or E (if not). STOP.
There's also the basic AD-BCE split here that helps you eliminate choices pretty quickly. The idea behind this split is that after you check the first statement, it's either sufficient (in which case your answer will be A or D) or insufficient (in which case you need to pick between B, C or E). This is useful especially when you need to guess, since you can eliminate a few choices and therefore increase your chances of getting it right.
3. DO NOT solve the question. You are simply asked to state whether the information is sufficient or not. You don't need to provide a definite, numeric answer! Don't waste your time with this, but rather focus on other stuff!
You'll see, DS gets a lot easier once you practice more and get used to the format. It took me a while too!
