crash323,
The questions on the RAF OASC website are of the easier sort. If you want to be sh1t hot at s/d/t then download the taskbook from
Flight Aptitude Test Guide for RAF OASC Cranwell FATS - it's only about £6 they are a lot harder and incorporate some fuel burn questions and get you thinking about multiple factors in one question.
i.e. Two aircraft travelling to Waypoint Z. One aircraft 75 miles away travelling 450 mph, second aircraft 50 miles away travelling 550mph. Who will get there quicker and by how much?
Also, there is a decent diagrammatic practice book on amazon. That too is only about £6. The questions aren't exactly like you get at stage one but they do get you used to shifting shapes around in your head.
Best of luck!