Originally Posted by Wooderson

You haven't said what you don't like about the current fork, or what you're trying to achieve with the new fork.

Speeding up the rebound makes shocks bouncy, like a pogo stick. Shocks will feel smoother if you slow down the rebound. You don't want to go so slow that it can't recover between hits.

Like someone else said, you can probably change out the coil, and sometimes you can get spacers to increase stiffness.

It just depends on what you're after.

As for tires, that depends on the terrain type and your riding style, but a fatter tire (if you have space) will improve traction and comfort, which sort of goes hand in hand with the fork. If you're not running tubeless yet, that's a consideration as well (assuming your rims are compatible).