Input devices are the mainstay of gaming. Here are some brief guides to find out what you need. Do research further if you want more information.
Unless you're playing some text adventure, chances are what you're playing requires a mouse, or something of the sort. Though many gaming mice exist, the characteristics to look out for are shape and sensor. Mice reviews and guides are available at the following:
Logitech G102/G203 (current)
A good mouse released by Logitech, having the same shape as their G Pro at a fraction of the cost. It has a "perfect" sensor. Available for around $20-30.
Logitech Optical USB Mouse (discontinued)
The predecessor to the M100 and B100, it is a 400 dpi optical mouse with a low maximum tracking speed. Despite this, it is pretty decent from my experience at the speeds in which it does work.
Coolermaster Storm Spawn (discontinued)
An unusually shaped mouse optimized for right handed claw grip users. Comes in three DPI steps: 800/1800/3500. Sadly mine began disconnecting randomly.
Logitech G9x (discontinued)
Yet another unusually shaped mouse. Uses a laser sensor, therefore it has innate acceleration that might be frowned upon. Mine had a badly frayed cable, therefore it stopped working.
Now that you've got a mouse, what would be the optimal settings? Firstly-DPI settings. After disabling acceleration OS-wide (do search how to-it is different for Windows/Linux/etc), you want to set a DPI that is reasonable for your resolution. If your res is say-1920 pixels wide, then a DPI of 800 or 1600 would be reasonable. If it is smaller, perhaps set it to 400. Either way, there is usually almost no reason to exceed say,1600 DPI, unless you like very small mouse movements. Next, you have to determine your ingame sensitivity (for playing FPS/TPS/etc). Find out a comfortable sensitivity which allows you to utilize your mousepad well. There you have it-you are ready to frag!
How would one maintain consistency across games though? Besides manually measuring inches/360 and experimenting, there are a few tools which help. Kovaak's Sensitivity Matcher allows you to match sensitivites across games. There is mouse-sensitivity.com, however some games are paywalled. Ultimately, choose the tool you like, and enjoy consistent aiming-no need to retrain muscle memory!
The mainstay of consoles, gamepads are preferable and superior for anything that does not require you to aim or click on the screen. For PC, your best bet is a XInput controller, which derives its control system from the Xbox 360 Controller. Older games may require DirectInput, so be aware of this.
The beauty of the PC as a platform is that it allows the most aspie-tier attention to detail people to emulate their favorite experience. Flight sims have advanced joystick and throttle controls, driving/racing sims have specialized wheels.