Just keep practising.
Pubs are perfect for learning how to aim. Even when some people's movement is terrible it will remind you to actually think about your aim when you miss that one scout that's standing still whilst shooting his soda popper across the map
I like sniping on cp_orange and ctf_turbine for practise but you can learn on any map. Though unrelated to aim you should always think about sightlines and positioning. If you use those right you'll be a lot more comfortable with the shots you take which will help your aim
Be comfortable with the sensitivity you use. You can learn to snipe with any sensitivity so use whatever feels good for you. If you feel like you're too inconsistent try messing with zoom_sensitivity_ratio a bit before you change your overall sensitivity (assuming you don't use a seperate sensitivity for sniper. No point in changing your sens on all classes just for sniping)
I still change my sensitivities daily but I use seperate sensitivities for hitscan/projectiles so I don't have to get used to it on every class every time. I feel like changing a sensitivity (both general sensitivity and zoom_sensitivity_ratio) by up to 20% is still comfortable to use and you get used to it quickly. So if you really want to start messing with sensitivities because you don't feel consistent enough don't change it by too much every time
There's no 'best' way of aiming. Learn both tracking and flicking. You'll naturally learn when to use what. I often use a combination of both with every shot I take
I prefer having my crosshair on when zoomed but I know some good snipers that don't use it. Though I do think having it on helps your aim it definitely isn't required for improving
Some minor things that helped me when I was still learning to aim:
- Go for every shot. Even when your target goes behind a wall. Shoot the wall. Doesn't matter. As long as you go for the shot and it's where you predict them to be it'll help you
- Avoid sniper v sniper servers. It's where I started when I decided to main sniper but looking back it really wasn't good. Most players there are bad and you'll learn bad habits like secondscoping. Secondscoping is bad because you're just shooting targets that are standing still. It doesn't help your aim that much and only works against other snipers
- Always keep your crosshair at head height when not zoomed in. You'll only have to move your crosshair horizontally in a lot of situations so this definitely helps
edit:
- Another minor tip: A great way to practise tracking is by tracking teammates. This works on any class. I often do it on scout too. No enemies around? Just track some teammates' heads. No need to shoot at them. Just stay on target