A lot of factors come into a mouse, especially one that needs to meet the precision of competitive CSGO gaming. Being one of the most important human interface devices, you should choose a mouse that suits you, and your needs.
The thing about CSGO is that when you use a device to do an action, such as aim, stutter-step, or even just to engage, you build up a muscle memory. This determines your ability in competitive with experience and skill. When you change certain aspects of input, such as Mouse sensitivity/DPI, Binds, and even the hardware itself (mouse, mouse-pad, keyboard), you alter your muscle memory, and how your brain operates when communicating with your body to create an action in game. Unfortunately, when altering these settings or hardware, you will have to "re-learn" how to do certain actions in game, such as aiming. When you buy a new mouse, it may take days to weeks for you too return to your previous level of aiming ability. Now, will buying a new mouse help with your overall aim? Perhaps, and I'll explain in detail...
When buying a gaming mouse, there are a few different key aspects you want to look for:
Does this mouse look like it will fit my needs, or is it too much?
This is a big one, you have different gaming mice made for different gaming specialties. You can spot them by looking at the sides and the top of the mouse. Does it have a shit ton of buttons on the side? That mouse is made for MMO's and MOBA's. The buttons are used as quick binds to activate different abilities, and some gamers use this instead of the keyboard, but it typically isn't used for CS:GO. However, my old Razer Naga had many buttons on the side that I used for binds in competitive TF2 back in the day (RIP) that made actions streamlined and easier than reaching fingers off the WASD keys to input a command. You can also use it for CS:GO for quick grenade access, but I don't recommend it unless you want too dedicate yourself to relearning grenade binds.
Are the specs up to par for competitive gaming?
When you use your mouse, you need to make sure that it will be able to handle simple tasks such as precise aiming from a distance, to 180 flicks accurately without any stutter. This is where you need to look to see what your mouse is packing exactly. You will be looking at the optical sensor, the "DPI", and the "polling rate". DPI for an FPS minimally should be around 800-1800MAX-DPI, and the polling rate should be at a minimum 500Hz for CS:GO.
Can you change the weight, feel, and/or look of the mouse?
Check the website or packaging for adverts such as adjustable weights, removable side and head plates, or software you can use to customize your mouse. I emphasize YOUR mouse because it is the mouse YOU are fragging with. Everyone is different, having the ability to change certain aspects of the mouse can give you the ability to experiment and find what is perfect for you.
Wired or Wireless?
Simply put, the technology nowadays makes booth of the streamless in terms of polling rate. A mouse’s polling rate is how often it reports its position to a computer. Both wired and wireless are nearly identical, except for the fact that if your mouse is wireless, it needs a battery. If you're not paying attention in the heat of a match, you may just end up with a low, or dead battery, causing troubles winning that 5v1 clutch. However, this is all personal preference, I would prefer the reliability of a wired mouse.
I currently use a Corsair M65 PRO RGB Mouse, it has two extra buttons on the top, one large thumb-button on the side, and two streamlined against the frame on the left side. I use the top buttons to change my DPI on the fly, the thumb button on the side to hold the lowest DPI for the smallest sensitivity, and two on the side for teamspeak, and toggling my walls muting teamspeak because goddamn the memes are too strong sometimes
Look for big brands the specialize in gaming mice such as Razer, Corsair, and (now) Logitech. Don't sell yourself short, yet, there is no need too buy a $200 mouse! Around $50 will get you a fantastic mouse with options too customize. Do some research online, check reviews, and if you can, go to a PC store to see the mice in person. Some stores will even have displays with the mice in the open, so you can physically feel the mouse and it's movements.
One last thing: GET. A. DECENT. GAMING. MOUSE-PAD. Don't buy a $2 mad catz xd 6x6 inch mouse-pad. Spend around $10, and get a larger mouse-pad if your desk can support it, and look into some CS-GO tutorial videos on training your sensitivity. You're mouse will perform much greater if use a decent mouse-pad, and you will love the difference.
You will not immediately get more skilled with a new mouse. You are going to get a bit frustrated at first, but trust me, download mouse AIM and TRAINING maps from the Steam Hub, play offline with bots, get a feel for your mouse, and practice, practice, practice. CS:GO is a highly physiological game, and it demands time and practice. Do your time, and you will be able to frag with the best of them.
Hope this helps, and quote or PM me if you have any questions~