Look for triangles everywhere. Go for a walk, look for all the triangles you can find in nature, then ask yourself what information you would need to calculate sides in those triangles. Don't come home until your brain is full of triangles.
if I can't see the shape that's being made I like to draw it 2d. But I really hate the amount of time wasted drawing triangles so now whenever I draw the diagrams I like to draw the axes on a diagonal and not like a flat out plane so I can see the shape stand.