To make a side cast tilt the casting plane of the overhead cast over to the side. Tilt the rod all the way over to the horizontal. It's a great way of throwing narrow forward loops, but it's most useful for casting in tight spots. Five benefits appear:

1. we don't have to take the rod up to the vertical where it's going to clunk on branches

2. our back loop can be kept low and parallel to the water and can be send underneath overhanging foliage behind us

3. the loop on the forward cast is horizontal, which is really useful for sending under branches

4. and we can keep this forward loop really low to the water

5. side casting helps keep the rod outside the fishes window of vision.

Side casting is also useful for casting into the teeth of a gale - for two reasons: one is that taking the rod high into the air allows it to get blown around and the other is that if our leader doesn't straighten out properly on the forward cast, it will simply land in a curve as opposed to a heap.

Side casting can be performed off both sides of the body, in order to cast of the left hand side for right-handers (or vice-versa) the recommended style is to rotate the wrist so that the palm of the hand is facing downwards.

Incidentally returning to that 40yrds of the wrong shoulder cast, doing this (i.e. putting the thumb behind the rod on the forward cast) makes this cast more acceptable to some instructors - aren't we a funny bunch?

A neat trick is the change of direction side cast. The way to achieve this is to perform the side cast as you normally would and then on the last forward cast just as the rod points in the direction you want to cast, rotate the wrist so that the reel points downwards. Many good stream anglers I know use this to good effect: they do a couple of false side casts to judge the right distance, and whack! change of direction, under the tree, dead on target.

Make sure that you point downwards with the rod tip on the final delivery, otherwise the line clashes with the rod...