The best way to increase performance in a game would be through upgrading your hardware.
If this is not a feasible option because of how stupidly expensive that can get, I would recommend doing the following if you haven't already:
1. Close pretty much everything but the game you're playing. Unless it's entirely necessary, don't have it open. This will just eat into system resources that could be used for whatever game you're playing. 2. Edit your settings in-game. If you're getting a low FPS, try decreasing render distance, texture quality, or any other graphics settings. If your computer is struggling to run it with settings on high, tick them back a little bit. 3. If you're playing on a laptop, make sure you're running on performance mode instead of battery saving.
Without upgrading hardware (And if you're running windows): Select "High Performance" in power options Close unnecessary apps that aren't required while gaming Have the latest graphics drivers Depending on the game, go in the settings and lower overall graphics options and disable vsync Go into the games configuration and make changes there (Youtube tutorials can be found) In task manager, set the task priority of the game to "High", if you don't know how to do this then you can find videos on how to do so on youtube.
Overclock your CPU and Graphics card if supported (Plenty of tutorials online) (Keep in mind it might decrease the lifespan)
Upgrading hardware: Get more ram (8gb ram for most games should be fine but some newer games are a bit more demanding so you should consider getting 16gb instead) Get a good graphics card and CPU (Make sure you have a motherboard that supports the CPU and Graphics card you choose and make sure you have a big enough power supply.) Make sure you have a look at game requirements for games you like (Don't go overkill)
Really depends. Sometimes it's software issues, sometimes bad optimisation of the program or game your are using, and sometimes your hardware is simply not good enough.