Take βίος for "life " or δένδρον for "tree".
You think of life and call it βίος (bio-logy, bio-chemistry....), a hard βίος, or a really nice one and so on.
You look at a tree or think of one you've seen, a big one, small one, dead-looking one .... and each time call it  δένδρον  instead. Easy.
What about the more difficult words, the ones that keep on eluding us. Use your imagination, creativity, call it what you want.
Take this silly sounding example of mine. I could not for the life of me get  αὐτουργός  right. So I chopped it up into:

	αὐ	short for "ouch, that hurt! "
	τουρ	a tour, round trip with a rolled "r " since it's Greek after all
	γός	the "gos " of gospel, for pronunciation.

Now I had the pronunciation, but no meaning for my pieced together creation. So I used it to label the man who tours his land and says ouch! (my back!, all that hard work!) and invokes God (or the gospel). It's long to explain, sounds completely loopy but is in fact quick, effective and fun.
So some people say:
That's completely stupid, αὐτουργός  comes from αὐτός meaning self and ἔργον meaning work, so we've got
self-worker
That is actually the correct definition, any manual worker (farmer of craftsman) who has to work himself, because he can't afford a host of slaves to do the work for him.
Like in this case, Dikaiopolis does own a slave, but he has to work himself as well.
By extension αὐτουργός refers to any free Athenian farmer.
Fine, but if you don't know the other two words and don't see why οσ + ε should become "ου"? (You will, a little later on, because it's all a question of ease of pronunciation, flow of speech. But you're not quite ready for that yet).
Just find your own personal way of remembering words. Use your imagination and apply everything you learn to reality: lived, read about, seen on TV. What doesn't make sense or can't be applied is useless, a waste of time. Concentrate on what you can understand, apply, use.