This expression that you have in your
IF is not really an expression. You just add 1 to
variablex and it should be true always, meaning that
DOTHIS is ran always.
variablex += 1
If structure in GameMaker
Say, you have variable
x and you need to know if its value is
if (x == 10)
x with other var increment:
if (x == y + 10)
I suggest that you read the manual once, to get some idea about programming in general. It's not easy stuff, but certainly nothing that you can't handle.
GameMaker manual - If statement