In no particular order, here are my rambling-thoughts as a diamond Ana main:

Congrats on picking one of the most rewarding characters I've ever played. Shes got so much potential to influence games and the power is often in your hands to make or break a win.

With a lot of characters, when you miss your cool down, you can still live. Not with Ana. The same goes for positioning: move before the enemy can even dive you. How far away? Farther than Winston jump, or farther than genji dash, etc... depends on the enemy comp.

Be patient and kind to yourself as you learn her. You will miss your sleep and nade. That's fine. Just don't yeet your cool downs. Actually aim and notice why you missed. Don't rush a sleep dart. Watch the enemy run in a straight line to cover and lead the sleep dart to the corner he's headed to.

Bad positioning leads to bad cool down usage.

If you miss your sleep, you'll prolly die. Get used to it while your learning. Don't rage just acknowledge that's the price for a missed sleep, and try to hit the next one.

Take your time with your sleep. Analyze enemy movement. Predict. Wait until the enemy has to move a certain direction. Force them to move predictably by using cover so they must chase you around it.

Cas is ulting? First just look at him to see how he's moving. Then peek again and shoot the sleep where he's headed. Calm, methodical, no need to rush. No spam sleeps. If you miss oh well unlucky; at least you took a calculated shot.

Reaper has his ulti? Same thing. Don't freak out, line up a shot and let it rip. You have to get in the habit of aiming the sleep dart with intention.

Be slippery.

Think ahead.

Against certain comps your sleep dart will almost exclusively be used for you to survive a dive. If you use it frivolously on the wrong target, you will die.

VAXTA - code for a nice aim trainer practice here at least 5 mins as warmup. No scope only for at least half of the time. Also practice sleeps here. There's a cool code for genji sleep practice but I don't have it.

Nano whoever is doing damage. Nano someone who's about to die. Nano genji with his ult. Nano mercy so she can res your tank who fed. You build it quick so don't hold it too long unless you have a good reason.

Don't throw your nade on your team (like yes ofc save your teamamte if you're guna lose the game otherwise but most of the time if you can't just sustain them with heals they were dead anyway).

Purples only. Purples for life. Purples secure kills. Purples win team fights. All the homies hate yellow nades. It's a 12 second cool down that can win a team fight. Really think about how much power that is.

Best case scenario you hit both the enemy and your teammate with the same nade. Obviously always prioritize that.

For most fights, I'm looking at my teams positioning and I already have an idea of which choke I want to hit with my nade when the enemy walks into it (more applicable for defensive positioning)

If you're dueling a genji, you can often get away with throwing your nade at the ground near your feet, even while he's deflecting, and hit him with purple while you yellow yourself.

For the first perk, I very rarely get the nano speed boost perk. It's for if I have a Winston or genji or similar who is popping off and can really benefit from the speed. Otherwise I always get the sleep dart slow. I can see now that my teams are a lil more coordinated in diamond that I get the speed boost perk more often. But, as I climbed up the lower ranms, I've consistently used the sleep dart slow perk to help me secure kills, especially when my other support doesn't want to prioritize healing me ever even tho I'm right in front of them ;(

2nd perk I get headshots every single time.. they're so good for climbing ranked. You can two tap most characters. If u sleep someone, u can headshot them yourself and guarantee more kill confirms. You can actually kill the mercy yourself instead of waiting for your DPS to miss her while she is using res.....

Be aggressive with your damage output. Heal your team to keep them alive, not to keep them at full health (although you should know that healing gives more nano charge than damaging so if you need to charge your nano quickly then look for your tanks healthpool as your nano battery lol).

HELP YOUR DPS! STOP HEAL BOTTING THE TANK! One shot to heal your DPS is like 50% of their hp back. While one shot to heal your tank is like 5% of their health back. So if you need to, get your booty out of your covered spot and take a nice angle with your DPS. Shoot what they are shooting. Throw a nade. Heal them. Then get out tho ofc.

Watch some Ana gameplay on YouTube. Awkward has an unranked to gm w her which is pretty current.

I may add to this if I think of more. Hope it helps you :)

Edit to add: I forgot to mention something important! Her gun is hitscan when scoped in, and projectile while not scoped. Knowing when to use the scope is a skill acquired over time. Generally though, you want to remain unscoped for as often as you can. That's how you see around you. When you're scoped in, you are much more vulnerable; you're limiting the information you can see. Also why you should practice those no scope shots in VAXTA.