Do not use short vaiable names except those with generic use (s for string, c for char, i for integer). The readability has higher priority than the speed of initial typing. We have intellisense so later it doesn't matter that variable is longer. It however simplifies reading and makes the code self-commenting.

Examples of how not to do it:

var res = service.GetFileData();

Now is it a response or a result? You could argue that if var wasn't used, it would have been obvious. But var isn't the problem. Incorrect naming is.