I study games from books, and would like to retain some of them in my memory, especially the opening part. I also want to remember my own games (I play about 5-10 tournament games - mostly against >2000 ELO rated players, and some rapid ones here and there). Are there any particular techniques or tips?
In my experience, memorization of chess games simply came from improvement. I first realized that I could remember the games of past tournaments when I was around 1600 ELO, and as I improved my visualization became sharper and I could recall games played years ago. My advice to you is to have the games notated and not just read, but play through them regularly. This repeated process of playing the moves of a game will help you retain the information necessary for you to recall the game in the future.
Memorizing things move by move is very hard indeed. There's evidence that masters use something called chunking. Google chess masters chunking to see various links. A basic example would be instead of Nxd5 Bxd5 Bxd5 cxd5, you might think "everything is exchanged on d5." Masters might think "OK, we set up the King's Indian formation."
Once you understand basic structures and motifs, memorization will be easier. Until then, it may feel like studying for a test in a class you don't like.
In chess, memory is related to learning. The deeper you study, the easier it is to remember the most important points. Its about quality not quantity. You can "cram" openings, but unless you understand the position you'll start making mistakes. You'll play better if you focus on the types of positions that interest you.
There are a few techniques to remember openings -
In the beginning, stick to a single opening. Ex: play only
Choose an opening that has fewer variations or that has (more or less) standard set of moves. For ex: King's Indian Defense or Sicilain Dragon variation. You can mostly play standard moves without worrying about white's moves.
Study common traps in your opening
Last (but not the least) - practice. Study more games and play often.
I found that flashcards are a great tool to help memorize complete games and game openings. They allow one to implement in practice many concepts mentioned in earlier answers.
There are many flashcard software available, including free ones. Some allow to schedule future reviews based on the difficulty of a recall. The idea is to drill difficult moves more often then easier ones.
A single flashcard could be created by taking a screen shot of a particular game position and inserting it in the question part of a flashcard. The answer part will contain the screen print of the next position of a game.
One potential drawback of this method is that it can be time consuming. A game containining 70 moves will require 140 screenshots. There are ways to streamline it and even fully automate it. For example this website will create chess flashcards automatically out of a game saved in Portable Game Notation (PGN) file. Full disclosure: I am the author of this website.
Maybe just write the openings and some games down and read them very often. Just hang them up on some mirror, for example in the bathroom and then every time you brush your teeth, you see it and will remind it. You could probably also hang some post its on your cupboard / desk.
On the openings part, just play your opening often and then you will automatically remember it.