Data sufficiency (DS) is by far the trickiest section for anyone starting the GMAT preparation. Here are some tips to tackle this section:
1) Know your choices:
Let's start with something basic. You should know how to use the choices. See the table below:
Choice A: Statement 1 is sufficient, Statement 2 is insufficient
Choice B: Statement 1 is insufficient, Statement 2 is sufficient
Choice C: Statement 1 is insufficient, Statement 2 is insufficient, Combined is sufficient
Choice D: Statement 1 is sufficient, Statement 2 is sufficient
Choice E: Statement 1 is insufficient, Statement 2 is insufficient, Combined is insufficient
2) Zoom in on the question:
There are two parts of the DS questions - facts and question. The best technique is to draw a box on paper and put the question in there so you separate the facts from question.
3) Simplify the question and facts:
Sometimes we are asked a complex question e.g. 3x-y<0? Try to simplify it, so you can keep noise away. So in this case this will be 3x<y. Similarly simplify the facts as well.
Before solving the question be very clear about what is being asked. See the question below:
[x] represents the least integer equal or greater than x. Is [x] = 0?
To achieve clarity, the best trick is to plug in numbers to see how the brackets work 
 = 1 as you can see based on definition, here x = 1, so we need to find the least integer equal or greater than 1. Not very helpful was it. That means we should try non-integers.
[1.9] = 2, as 2 is the least integer greater than 1.9
[1.1] = 2, again 2 is the least integer greater than 1.1
Now I am clear what the brackets mean. Imagine x on a number line. If x is a fraction then, [x] is the integer on the right side of x on the number line.
So what does [x] = 0 mean? This means that -1<x<=0, because I imagine x to be a fraction less than 0 but greater than 1, so a [x] will give us a 0 i.e. the least integer greater than x.
The question box in this case will be: