You'll obviously want to give it the HM Surf. Earthquake (TM 26) is also a must, and you can find it in the hidden part of Wayward Cave (the entrance hidden under the Route 206 bridge, where you find Gible). Unless you've got an Ice-type, give it Ice Beam (TM 13) which is on Route 216 (you'll need to defeat Candice and use Rock Climb to reach it).
As for level-up moves, it doesn't get much. Muddy Water at 41 and Recover at 54 are the only notable ones, and Muddy Water is redundant if you have Surf.