One thing you can use is Gunnar glasses which will lessen your eye strain and lower the blue light that you see, enabling you to see better while gaming. Gunnar glasses come in a variety of colors and styles but you can find a pair for about 50-100 dollars. Many professional gamers use gunnar glasses and some are even sponsored by them.
Another accessory you can use for controllers is Kontrol Freek thumbstick extenders. Kontrol Freek accessories will allow you to better control your game without raising the sensitivity in the settings high. They are fairly inexpensive as well, ranging from 10-20 dollars. Professional gamers use Kontrol Freek thumbstick extenders as well, they can be used with PS3 or Xbox controllers as well.
If you are playing a first person or third person shooter there are some tips to help you do better in a firefight, especially online. Movement is an excellent way to avoid being hit when in a firefight. By movement i mean, running, crouching, “dolphin diving” and looking around for opponents. Dolphin diving is the process of going from standing up to prone, which is useful when spawning, and as soon as you are being fired at. Looking around corners and checking behind you is also a good idea as well, filling gaps in areas your team has not moved to is a good idea as well.
When sniping its a good idea to aim for the head first but if not shoot for the chest. Automatic weapons get better accuracy at long range when you use burst fire, either using three round bursts or changing the firing mode. Using good cover when firing or sniping is a good idea as well. Look for either rocks, foliage, or trees to break up your profile making it harder to see or find you. Stand back a few feet when sniping from either a window or a top of a building, it makes it harder for people to find you and shoot at you.