Buy a copy of The Poor Man's James Bond and have a go at making everything in it at least once. Scatter these devices around prominent public buildings in your area and then diffuse them whilst wearing a face shield; make sure you phone in bomb threats first so you have a realistic environment to work in. If the local plod enquire what you're up to direct them to this thread.
Or just read the newspapers to keep up with current affairs and wait for the army to teach you what you need to know rather than turning up with a headful of Chris Ryan.
I'm not really qualified so don't take my word but one suggestion should be to do some research and get a basic idea of the structure of the unit you want to join, ranks, and what you plan to work on. The army will teach the last 1 but it doesn't hurt