The grapple feat chain will increase your grapple CMB, and are the easiest way to obtain a bonus on your checks:
- Improved Grapple: +2 on grapple checks and CMD against grapples. But this requires improved unarmed strike, or dirty fighting (see bellow).
- Greater Grapple: An additional +2 on grapple checks.
There are also a few other feats that can increase your CMB on grapple attempts:
- Powerful Shape (requires druid 8): Grants a bonus on CMB and CMD as if your size was one cathegory larger while in Wild Shape.
- Unfair Grip (requires power attack): You gain +1 bonus on grapple checks to maintain a grapple, while your enemies take -1 on their checks to escape your grapples.
- Kraken Style (requires BAB +3): Adds a +2 bonus on grapple checks to maintain a grapple.
- Dirty Fighting: This will either allow you to grapple without improved grapple while flanking, or increase your flanking bonus to +4 instead of +2 to initiate a grapple while flanking. Not only that, this feat will allow you to qualify for other feats as if you had Dex 13, Int 13, Combat Expertise, and Improved Unarmed Strike.
If you take Dirty Fighting, you can qualify for Improved Grapple as if you had Improved Unarmed Strike, making the feat unnecessary, while still granting a bonus on grapple checks. The only thing missing for Kraken Style would be BAB +3 then, as you would already have the other requeriments. Unfair Grip would still require Power Attack though.
The feat Additional Traits, if traits are allowed by your GM, can grant you access to two religion traits that increase your grapple CMB:
Keep in mind that both grant trait bonuses and will not stack.
Turn into creatures that can grab foes
The grab special monster ability grants a +4 bonus on grapple checks to maintain or start a grapple.