[Cr3aTor]

Do what I like to call "practice runs".

It's a simulated-like attack, whereby you research your target, formulate and prepare your method based on your findings and execute your attack (on your target) thereafter. It Is not the real deal. The objective Is to establish how they operate Internally, the questions asked, how they expect to be answered and most Importantly, the vulnerabilities of the representative(s).

Repeat the process on various organizations- to get the experience, confidence and skill set In preparation for your real SE.

I couldn't say it better !

However in addition to what was said above, I wanted to say that you could also practice on your friends, family, etc (of course with no harm) . Learn psychology and try to induce some reactions, behavior, feelings, etc of your target. Make him/her think something about you while you are gathering other details about them. Analyze, observe and be vigilant of your surroundings. Or even try to get into a place where you don't belong by pretending to be someone else, basically something like @mothered said. (a school, in a kitchen of a restaurant, etc)
I think that if you know how humans react, feel and behave in general, SE is not that hard.