How do I know which SUVAT equation to use?

SUVAT equations link the variables S (displacement), U (initial speed), V(final speed), A(accelerations), and T (time), for situations where there is constant acceleration. Each of the 5 SUVAT equations links 4 of these 5 variables together. You will usually need to find the value of 1 variable, using 3 other variable values that are given. To do this you need an equation that has only the 4 variables you are concerned with in it.

As with most math/physics problems, clearly laying out the information you have, and you need is very helpful. I suggest at the start of each question you list the 3 variables you are given values for, and what you have been asked to find. This list will make spotting which equation has only the 4 variables you are concerned with in it easier. Initially this will be a slow process, but with practise the correct equation to use will become obvious. You can practise on this website - http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/MEI/MechSuvatEquns.html