screenshake, zooming, tilting, wiggling/wobbling (hand-held camera)
tweening everyhwere (don’t be afraid to use lerp, sometimes it looks good), numeric springing
make stuff that doesn’t have to be static dynamic - like decoration and backgrounds
post-fx - filters, shaders, overlays… go wild (moderately)
randomisation everywhere! - sound pitching, different sfx variations (where it’s suitable), particle effects, colour tinting, names for stuff, dialogue, game over screens… again, just go wild with stuff you can’t possibly break gameplay with
audio panning if you’re doing action games
pretty UI elements - score interpolation (have a separate variable that slowly tweens to actual score and draw that), you can also prepend zeroes to it (this works best if you use a monospace font)…
speaking of fonts, use your own if you’re trying to include yourself more into your games
transitions (fade in/out, etc… DON’T MAKE STUFF STOP MOVING IN-BETWEEN TRANSITIONS, IT BREAKS THE IMMERSION), this also applies to audio, don’t just suddenly stop your music/ambience
procedurally generated stuff can be awesome if you know what you’re doing
choose a colour scheme and/or palette and stick to it
audio/visual cues are better than tons of text
Basically, the bare minimum you need is tweening and variations.
Feel free to add to this list, I can’t think of anything else right now.
Juice it or lose it - a talk by Martin Jonasson & Petri Purho
Jan Willem Nijman - Vlambeer - “The art of screenshake”
Rapid Game Design by Cactus
Moleman 2 - Demoscene - The Art of the Algorithms (2012) - making art with code