What's the key to solving simultaneous equations?

With simultaneous equations, a lot of the maths GCSE qualification, the best approach is to work things out step by step and write every step you take down on your exam paper. This does seem like its time consuming and tedious but it always helps my mind follow through on the method that I'm using to solve the equation. I always approach simultaneous equations with the impression that I will solve them by substitution, and use the elimination method where I've spotted that it can be done easily.
When I was in school many students tried to use the elimination method as a way of avoiding substituting because they're under the impression that it is more difficult. Though it is the may be the more difficult method, substituting can help you solve almost any simultaneous equation. Practice solving equations by substitution (remember the key is to write every step you do) and simultaneous equations will become second nature in maths.