After being close to rank 100, I'll compile things that worked for me toi catch up and be done with PvP for the forseeable future.
Other's people tips work too,

That said, my list is from (and for) someone who doesn't really like PvP, but still would like to get rewards and be done with it for the rest of the season.

Some of those are quite obvious.
Some are not.
Some are just my observations.
Some are just tips for newer players.

What counts for Veterancy
As others mentioned: AP and Experience earned in PvP. First victory of the day for a character also counts for it, and - from what I've seen - it's affected by both AP, Experience scrolls, and - if in Cyrodiil - delve boss buff (kill a boss in a Delve in Cyrodiil to get it for an hour)
Progress is account wide, so that's a blessing because...

Having multiple characters help greatly...
I have 8 characters, including one I was leveling.
Each character is a bonus experience for first PvP victory, crucial for "burst periods" (more about it later), even if they are not PvP oriented.
I didn't change my builds all that much, but I increased their HP to at least 20k across all of them.
Helps with survivability, and I noticed absolute teapots leave you alone with that much health; anything below and they get salty (in my experience)

...but not all of them will win withotu sacrifices
Which is the ugly truth.
RP, PvE, or just "vibe" builds may or may not perform in a way that will allow you to win that daily reliably.
But that's allright. It all relies on people you're queued with. Sometimes my "vibebuilt" characters got their victories cause they were carried.
It's a good idea to have at least one or two characters that perform well in PvP, such as tanky healers or high-DPS killers; I'm of the former rather than latter.

Having a nice score helps
Points and medals earned during the match contribute to the final XP reward. Higher personal performance = more XP.
Kills yearn much better scores, but that's not the only thing.
You earn scores for almost everything; including DoTs on enemies and HoTs on allies.
My tank-healer earns himself a lot of AP for spamming heals, and my DoT/HoT character as well, without actually killing anyone.

The worst thing you can do is queue and go AFK/do nothing.
Even if your team has such a teapot, don't step to their level and just finish the match with honor.

Try getting at least one rank per day
Or more if you're up for it, especially at earlier levels when you'll earn multiple per day across your characters.
Such pace pays off later at higher ranks where more EXP is needed to level up.
And pays off much later when you reach the rewards you want and never have to touch it again until new season.

Burst periods
Unless ZOS changes something, much like during Deathmatch spotlight event this post is written during, be it a victory or loss you will earn your daily exp rewards.
PvP Spotlights and Mayhems are your best opportunities, and any other events that boost PvP EXP.
Afking is still a bad idea during this, because you miss out on additional points scores and medals give, so even if you're "vibebuilding" just go out there and do something; heal, place DoT, deal some damage, capture point
.
That's where having multiple characters helps a lot, even if you're still leveling characters.
Queue with each one and grab that victory bonus.
Just make sure you queue to the right event.

Additional help
If I had to do it again, I'd stockpile on AP scrolls and use them after reaching higher ranks where queueing multiple times gives you one rank.
But, as we say in Poland: a Pole is wiser after the damage is done.
You can also save the stock for the burst periods, especially the grand ones.
I didn't use tortes cause only today I maxed out Provisioning, so I can't speak on them.

Its worth to use those boosts on best performing characters of yours, but also on the ones you're leveling.

Take advantage of the chaos
After Update 51, the nerfs will hit DKs and WWs (probably).
But as of now they are still absurdly well performing characters regardless of build or skill.
Like, really, playing WW now requires zero skill.

It's nice to keep an ear to the ground, or have your eyes peeled, for type of characters or builds people are running and demolishing others.
I happen to have a WW and a DK and those two have priority in using those boosts.
I can wipe the tears of shame with the skins from Veterancy later.

About Cirodiil
I've heard it years the most experience, especially in organised groups and firing balistas, but I pretty much play solo (no guild or friends; shocking, I know) and to me it consumed more time returning less progress compared to just queueing BGs.
I had a bit better yeild when I joined some random group as a healer than my WW tho.

If you have a guild that runs Cyridiil groups, join them for a while and see how it feels.

I think that's all what i have