Prep all sides in advance.
We have a giant tin bath that we fill with ice and chuck drinks in there so people can help themselves.
Have a table with sauces, napkins, cutlery, glasses/paper cups away from the BBQ so people can go back and forth as needed.
Get your phone hooked up to a Bluetooth speaker and have a few playlists ready.
Set out plenty of chairs and if you have anything you can use as side tables, set them out too so people have places to put plates/drinks.
You can always pre cook some basics (sausages/chicken skewers) and have them ready when people arrive.
Once everything is prepped and set up, shower and get yourself ready. Come down, get a drink and start cooking the first (or second) batch of food.
When it’s done, circulate a bit, chat, put batch 2 on, chat more, once it’s done, do the same. I’d try and limit it to 3 batches of food max - then announce food is all cooked, get yourself a plate, chat, socialise etc.
Put food waste and a bin ready so you can bin things outside (seems mad to carry it inside, bin and carry the waste back outside).
Have a clear worktop space you can pile up the empty plates (or use paper and put them straight in the bin) and sauces etc. Leave all clearing until everyone’s gone home - just bring stuff in and walk back out with puddings/something sweet.
Finally, relax! Unless your friends are particularly picky no one will care if there’s a wait for food or things don’t run smoothly (in our house generally DH does the bbq but inevitably he’ll get distracted and one of our friends will take over, the drinks run out and people end up going inside to help themselves etc).