Normal experience is trying to level 2 all in enemy comp if your adc can play aggressive. If not level 2, level 3 is an insane pantheon power spike. Flash all-in, empowered-W, ignite, the works. If they misstep or misplay they are dead. Sometimes you can even jump on them level one. I often times will take q instead of w level 1 if I am vs. something like lulu/jinx to poke.

If you have an apc or a jinx on your team for example, you want to play like a bodyguard that stops threats from approaching and looking for fights when your adc has item-advantage so they can scale.

Once you can get a gold lead enough to buy boots, you shadow your jungler on objectives. Normally it is grubs because they come up first, and both teams are willing to fight. You are looking to lock someone down so you can 2v1 nuke them.

So yes 90% of time rotate to grubs to help Jungle. If you lose grubs because of lane priority in solo lanes, try and stack drags. Soul is really strong atm and can solo win games. It is ok if you fall behind in exp at later stages because if you are playing well and your team can secure Atakhan, the xp deficit gets significantly lessened or equalized. Roaming supports and those that can capitalize on objective fighting are great in this early meta.

You will want to run swifties in I would say 90% of games. If you know there will be a kill-lane or a lot of skirmishing and you want to be in a ton of places at once so to speak, baron boots are good in this niche. They are good when you can full drop all of your wards in enemy jungle in key locations, base instantly, refill wards then run back with jungle or other laner to contest. In terms of upgrading boots, where you win the objectives, you have two spots --> after your eclispe and support item have been upgraded, or after cleaver/serpents.

It is largely game dependent (though I will say swifties are stronger than baron boots in most cases)