There are several things you need to consider. If he's going to be carrying them around for any period of time then the weight is important. You don't necessarily want to go for the ones with the highest magnification as they don't always give the best image. Go for something between 8 and 10x as above 10x will need a tripod. You also need to decide on the diameter of the lense as this effects how much light enters the binoculars and the clarity of the image. If he's going to be using them in poor light then a wider diameter will be best. However anything wider than 50mm will be quite heavy to hold.
Another thing you need to look at is the 'field of view' - this is how much you can see through the binoculars and is usually given as the number of feet visable from 1000 yards. If he will be using it on board a boat then a waterproof pair would be a good idea.
If you are not sure of what he wants then the best idea is to go for something that will suit many needs. Something between 8x42 and 10x50. Bushnell are a good make and are quite reasonably priced. I have the Bushnell Natureview 8x42 and I'm really pleased with them. I bought them for looking at wildlife while we are camping and they are easy to use, compact and quire light.
If you have a Jessops near you then they are really helpful and I think they have a slae on at the moment.