When Playing Against Someone Who Doesn't Have Openings Memorized

If I know the person I am playing (e.g., a friend or someone with whom I am familiar) does not have openings memorized, will it do me any good to try to memorize and use that theory against them? For example, I have a friend who always starts with e4. He knows some opening principles and gives me a good game. Am I wasting my time when I try to play back with, for example, a Sicilian defense since he will be quickly out of book? That is just one example. Is learning some openings only useful if I will be playing very advanced people? I already know general opening principles. Control center, develop minor pieces, don't waste tempi moving the same piece twice in a row in the opening unless you have a good reason, castle early, blah blah blah...

This course by GM Shankland might give you some ideas:

http://www.chess.com/chessmentor/view_course?id=334

It's called Exploiting Typical Opening Errors.  You raise a good point about the validity of opening study though.  Just memorizing opening lines isn't enough unless you understand the ideas behind the moves.  If you know the typical plans for each side then you can adapt and perhaps punish your opponent for strange moves. One of the main ideas of the Sicilian is to get an unbalanced position so no, I don't think you're wasting your time playing it. There's so much theory available that even if you study a lot, there will still be lines you don't know about.  If you like the positions you get you should play it.  If you don't, then don't play it. My 2 cents.

You could consider some tricky lines, even if they are dubious or even refuted. Several gambits for example, can be difficult to play and find compensation against somebody who knows the "right" answer. But they can be brutal against somebody who plays intuitively, even if he respects opening principles.

just play your normal openings and opening lines and when he starts to play non-theory moves, dont try to punish him immediatly, just play normal and reasonable developing moves. 

You'll be in a really good spot assuming you know the ideas behind your openings.  You could go for sharp lines but beware that they have a chance to calculate through them, but that's work and time they'll need whereas you'd likely know the theory beforehand. 

you do not need to learn any openings but of course it helps. i do not know my openings.  i just like to make stuff up to get my opponent out of their comfort zone.  

i heard that in the armenian chess schools they learn middlegames and endgames and do many tactical puzzles.

of course when u do not know your openings your options are a bit limited sometimes.  the goal is to have a plan to come out of the opening with an easy plan with each of your opponent's options, u do not need to know a lot of theory to do that.

i liked david pruess's development and planning series and i mostly forget it; it's an old series but quite good.  any opening is fine if you have a plan.  i'm not a fan of playing race positions (for instance yugoslav attack dragon if not updated on the theory bc opponents can win games simply by knowing theory sometimes, i prefer playing a game of chess.  to each their own; you can find a lot of ideas in chess whatever you choose).  every system has it's strong and weak points.

The typical advise is to spend 50% of your time studying tactics, 25% on endgame and 25% on openings (or something close to that). When studying openings you are merely adding to your overall chess knowledge. You are learning how to get to the middlegame without losing along the way.

When analysing an opening I think it's important to take a good look at the first few moves (I mean move #1, move #2 and move #3) in light of the objectives of the opening and ask "why" and "why not". But gaining a "deep" understanding of an opening can take years.

It's not likely that you will actually see many of the lines you study in actual play. Most games go out of book in fewer than 10 moves; many in less than 5. I have read many book writers (GMs, FMs, etc) say that for many years they played a particular opening almost exclusively and I think that's a good idea as long as you don't turn your back on all the others.

Time and curiosity will lead you into many directions. With chess, after several years of studying, I often find myself saying to myself, "I think I am finally beginning to understand this game."

I use shapes e.g 5 block shapes or other principles like rotation. I never memorize openings simply because I have bad memory. If you know the shape and what you want to do with it, its easy.

There are many things one can do like taking the 'aura' of a shape.