Order of elements in a formula?
There's something called Hill System. This is the system of writing chemical formulas.
In this system the carbon atoms are first, then hydrogen atoms and then other in alphabetical order. When the formula contains no carbon or hydrogen atoms, then all the elements are sorted alphabetically.

source: http://en.wikipedia.org/wiki/Hill_system

So it should be: $\ce{CH4}$

However, the Hill system is not the only method of ordering elements in a chemical formula. We can instead choose to list the elements based on their electronegativity. ManishEarth explains this in his answer to this question.