Warming up in my opinion is vital. A lot of players neglect it and think that they don't need it, but I think that every player benefits from warming up. Contrary to popular belief warming up is not really about "waking up your muscle memory" or anything of the sort. It's no different from warming up for any other physical exercise. It helps you get comfortable, warms up your muscles and makes you less stiff. All of those things create consistency. Whenever you go to bed you get a little rusty, and warming up is like washing that rust off.
But there are some ways you can drastically increase the quality of your warmup, allowing you to warm up faster leaving you with more time to actually play the game. I would like to go over some of them today.
The first big problem is the difficulty of the warm up. A lot of players don't warm up properly, using areas like the practice range. Your warmup needs to be challenging, both physically and mentally. If you are standing still while you shoot bots, you won't really get warm very quickly. A good warm up needs to have erratically moving targets with small hitboxes that move around within 360 degrees around you. Your warmup needs to force you to move around a lot. If all your targets end up in 60 degree cone in front of you, you will struggle turning and your aim will get lazy. You really need to get to work, making big sweeps across your mousepad during your warmup, aiming at targets above and below you. You need to practice flicks of varying distances, and need to track targets at different speeds and from different distances. Make it difficult. Switch targets after every shot. Make a 180 degree turn after every shot, etc etc.
So once your warm up is prepared there are some things you can do outside of the game to help you get into it. Make sure that you are hydrated, if you aren't properly hydrated focussing and tracking targets with your eyes will become difficult, moving your arm around will be difficult, and you are more prone to mental fatigue meaning that you will go on autopilot faster. Doing a short workout before playing can also help. Just do 20-30 jumping jacks or something similar to get the circulation going. One uncommon tip is that you should really make sure that you don't masturbate, eat a lot or go to the toilet immediately before you play. All those things put you into a very relaxed state because your body feels safe, which means that playing the game will become harder. Don't let your brain think it can go into lazy mode.
So once you start the warm up itself after making sure you have a good warm up prepared and your body is physically ready as well, its important that you keep your brain busy. A lot of Counter Strike players for example figured out that keeping your brain busy while warming up is incredibly important. When you are playing the game itself you need to think about a lot of different things at once. This can be super stressful and it forces your aiming to turn subconcious. Now if you warm up in a custom game for example the issue is that there is nothing to focus on but aiming. This can give you a very false perception, because you feel like you are warmed up but only when you can 100% focus on it. Once you go in game you either tunnel really hard on your aim to maintain it, stopping you from thinking your gameplan through, or you are thinking about your gameplan but your aim will go down the drain.
Thats why it's really important that you keep yourself busy while warming up. Some common techniques are listening to music while playing for example. Make sure that the music is complex and ideally has lyrics, and make sure that you follow the lyrics really hard. Ideally you can sing along the song in your head, just make sure that you are conciously listening to it. Don't let it turn into background noise. Ideally you should listen to music you have never heard before so your brain needs to think harder.
My favourite method is math. Now I know what you are thinking, this is probably really boring but it can help tremendously. Just have some math terms on your second monitor or on your phone laying in front of you or if you don't have those things on a piece of paper. While you warm up, you are going to go through each of the math questions and you try to solve them. I personally like to multiply two 2 digit numbers. I just go 17x36 and try to calculate the solution all while I am doing my warm up routine. If thats not hard enough for you, then you can go to 3 digit numbers, and eventually 4 digit numbers. Maybe you can use 3 variables instead of just 2 and so on and so on. Be creative. Forcing yourself to do math makes it nigh impossible to focus on aiming during your warmup, which forces your brain to use its muscle memory, which is what you want. The main reason most players have inconsistent aim, is because on some days they think way too hard about their aiming. Aiming is one of those things where not thinking about it is usually best. If you deliberately try practicing your aim then of course, you should think about it and nothing else. But if you are warming up or playing the game, you should let the subconcious do its thing.
Talking to people or listening to people talk can also really help. Having a Stream open in the background while doing math for example, or holding a conversation with friends during warm up can be a huge help and seriously improve the quality of your warm up routine.