Yeah right, nobody really gives an answer.

OK, first of all most items are just random, you should realize it (and there is nothing you can do about that, some can also be found in levels but only non rare ones), some items you get for reaching deeper levels (or beating the games) and some in PD(=Parallell Dimensions=Bonus Levels, blue teleportion levels, doors etc).
Atm just try to get every random item until you unblock it (after that you can leave the once that suck) and try to reach deep levels, because most of the PD's are too difficult at the beginning.
Here a list of PD's you should try/train from the beginning: Level 3, 6, 16.
You should avoid all others at the beginning.
If you beat the lemons (level 30) 10x and beat the bombinos you have perhaps the skills to enter PD23. If you have beaten PD23 you can ask again.
Also helpful:
zaxarinka.com(The items that can only be found non-randon are called "Coef. 0" items)