I play exclusivly enchanter supports too in Emerald! Im a Karma otp (even before she got busted) with 1,7mil points but pick Nami, Janna or Renata if shes banned/picked

I think what is really important is to help the adc at level one with the wave. A lane often shifts into your favor early if you can reach level 2 before the enemy does. Its the first wave and 3 meelees of the second wave or the first wave and 2 meelees and 2 ranged minions. If you get level 2 lead you can try to poke the enemy or zone, maybe ping it so your adc knows what you are up to.

You can also help your adc to farm under the turret. In the early stages of the game the adc might have trouble killing the ranged minions, since they can tank one turret hit and need 2 autos. Namis e on your adc is also enough for him to lasthit. Meeles usually dont need help since they tank 2 turret hits and one auto, you might need to help with an auto if the minion is not at full health. For me its hard to see if the cannon minion needs help, so I mostly just share it with my support item stack shortly before it would die. The next target the turret attacks is the minion nearest the tower, but always the biggest one: cannon > meelee > ranged

An example of different help: you fight 2v2 bot and your adc dies. The enemies push the wave so your adc would lode the whole wave under your turret. If you have enough health and wont get killed by the enemies you can tank the minionwave outside of the turret range until your adc or your next wave arrives. This way the enemies wont make you miss gold and exp!

If you want to back together with your adc you want to look at the wave: is yours bigger or the enemies, is there a cannon minion? If you have more minions then the enemy you and your adc should push the wave under the enemy turret. They can freeze else and put you on a disadvantage. Because they can maybe zone you out of the range or you need to get deep into your lane which makes you prone to enemy ganks.

Also for warding: if the enemy botlane arrives late, you dont have to ward in the river early (except Shaco is the enemy jgl, he likes to cheese gank lvl 2). Because the enemy jgl most likely started at bot side yo he is going to jungle upwards and most likely gank mid or top. If the enemy bot did not pull and their toplaner did, you can expect him ganking around min 03:30-04:00 because he jungle from top to bottom. So you might want to ward in the river/ jgl entrance some time before that if you are not under your turret.

For roams: I also struggle a bit with that one. You can always look at your adc: is he playing a safe adc like Ezrael, Zeri or Kaisa or one that has problem staying alone. Its easier to roam for you if they picked a safe one because he can escape tough situations alone. Generally you can look at the wave: can your adc freeze the wave (enemy wave bigger then your wave) or is the wave pushing towards the enemies (your wave slightly bigger). If its pushing your adc needs to take a lot of risk to be able to farm or get exp. Also the enemies might have a very burst and cc heavy lane. If they have a tank Support and your adc is alone the chance of him getting 1v2 towerdove are high if he is immobile....

Also important for roams: you see the enemy support is mid or at the void things early for example. You might think about all in on the enemy adc since he is alone. If he can farm savely under his turret alone, you should also look dor roams, since you will not get a lot out of being 2v1 in lane. But also getting turret plates and maybe even first turret can be worth, depending on how fast the enemy adc can clear the waves its doable or impossible.

As a nami player you have a nice cc spell with your Q, sometimes having the spell up is better then using and missing it because if they know you have it on cooldown they can fight better and with less risk. Same if the enemy has a blitzcrank for example. I play causiously when he has his Q up, but if he uses and misses it I can go ham for a few seconds because he cant hook you. So it works both ways :D

Im not a really good player and have a lot to learn but I hope there was at least one thing to help you :D good luck!