I've been lucky to spend a fair bit of time over the weekend enjoying The Witcher 3, I've managed to craft some Griffin swords & sell quite a lot of loot that I am now carrying around 10K in gold.
Sidequests & Contracts have been my main focus. Contracts are given to you by village noticeboards & usually involve you doing some investigative work before killing a monster.
The example below is The Merry Widow contract.
The various contracts you collect given you an expected level your character should be, anything coloured green is usually safe enough for you to give it an attempt.
When completing the contract you are normally rewarded with loot & gold from the person who issued the contract.