i never seem to have money in this game the most money i had a once was like 100 gold .

Selling the right things to the right people. If you pay attention there are items certain characters care about and will pay a higher price for.

Also in general, good equipment just sell that, and dismantle only the weaker stuff. You get about the same mats either way I think, so you might as well take the cash.

Um... pick up everything that's not nailed down and sell it :)

In Velen have a look for the horse riding and boxing challenges. Horse riding is self-explanatory. For boxing, just bet 50 each time and go into the fight. Do 2-3 hits, wait for the enemy to attack, dodge backwards and do another 2-3 hits. Easy money.