The simplest trick of them all is to read the stem, and then immediately start looking at the easier of two pieces of information, for example, if you get these two options:
1) x+y-6+2xy= 23
I used to go to 1) and analyze it. Now, I just pick the easier one to start, which in this case would be statement 2). When you are able to easily eliminate 1 of the statements, it gives you a decent confidence boost because you narrowed your choices down by 40-60%.
What is more interesting about the example above and something that most prep companies don't tell you is that IF YOU CORRECTLY GET ONLY ONE SOLUTION TO ONE OF THE STATEMENTS, THAT SOLUTION WILL AUTOMATICALLY BE A SOLUTION TO THE OTHER STATEMENT.
What is the value of x?
1) x is a prime factor of 221
2) 2x = 34
Clearly, the second statement is easier to evaluate (sufficient..only answer is 17)
If you know this, the first statement is much easier to evaluate because you KNOW that x=17 is a solution and you can immediately divide 221 by 17 to see what other factors it may have. (17*13 = 221)
Note that knowing the answer to one statement does not tell you how many solutions the other has, so it won't tell you directly "insufficient" or "sufficient", but it gives you at least one solution to start with.