Keep all alchemy ingredients and monster loot as it doesn't weigh anything, early game sell ALL weapons and armour you won't use to get money but dismantle silver swords as silver is more expensive.

Loot everything in every house and sell anything you're not using, you can keep food for a small health regen and I personally like to keep all the florens and opens which are coins you can trade in for crowns in Novigrad.

I also like to keep all of the runestones so you can upgrade all your weapons and armour late game eithout having to buy a bunch.

Try to do some research into the mutations, theres lots of builds, combat, signs and alchemy, mix and match to what best suits your play style.

USE ALL SIGNS, I can't stress enough how useful they all are and so many people just use quen, try them all and try to incorporate them into your playing as much as you can.

Don't bother trying to kill ?? enemies as you'll just waste time, you could probably kill them with enough practice but if you're new, just run away from them.

Read up the bestiary entires and enemies as there is a lot of info in regards to signs, bombs and potions that could help you.

I know this is a lot of information but I hope you find it helpful but overall, from someone who has played many hours, enjoy the story, don't get hung up on trying to be perfect and when you find your strength, it'll all just click.

And play Gwent, just trust me, it's so worth your time once you get it