Updated: Dec 16, 2019
Something that can be incredibly useful is to just sit down and play game. While playing, instead of focusing on the objective that needs done, wander around the scenes and look at everything that went into it. Once you have a general understanding of what is happening behind the scenes of a game and how it can be achieved, you will start to notice it during gameplay.
Diving into a large 3D game that has a little bit of exploration in it can let you see what everything interacts with one another. Whether that be when you get close to an enemy and they start to charge you, special effects when performing an ability, or going through portals, they all tie into how to build a game.
Another thing you can notice are errors or faults in design that one wouldn't normally experience. I've replayed games and noticed the smallest items that don't take away from the game, but was overlooked nonetheless. A character walking through boulders where there should be a collider or getting stuck in an unplayable area and not getting out.
Every game will have issues that go missed, and some happen only on very rare circumstances, but seeing them and fixing them is crucial to a good game. The beauty of buying and playing games means that you already have tools to know how to design a game. It could be you like the level design, the textures of an environment, or the smooth controls of the character.
Another interesting thing to try is playing remastered games that have had a face lift for the new age. Being able to play the original version of a game and then the enhanced version will really show the differences in how much detail was put into the game. The graphics and poly count on characters are usually the first thing that is noticed.