The ideal behind this build is to get accustomed to microing Misha. Honestly everything with playing Rexxar at a high level is based on your ability to micro Misha. If you have that down essentially the idea is to go back and forth between hitting wizard minions for globes, and keeping Misha in the faces of enemy heroes. You want to annoy them often as possible with stuns and slows. With this approach Misha will be a bit squishy in the early game but that goes away right at level 4. And its essentially all easy from there. A few things to remember....

1) Never get off of the regen globe grind. Hunter Gatherer is only as good as you allow it to be.
2) Once you hit level 7 Rexxar will become a bit of an issue on the mana front. Expect to burn through it.
3) Take full advantage of how handy the D key is for getting Misha out of tight spots.
4) Do not be shy with the Misha charge ability post 7. Its her best ability by far.
5) Do not be shy with the boars in team fights. The CC is extremely viable.
6) Jungling is still possible with this build but nowhere near as effective as it is with a Jungle build.
7) When Misha dies, Rexxar lives. When Rexxar dies, BOTH die. TAKE CARE WITH REXXAR.

You will be surprised with how much damage you will be able to both soak and dish out with this build. Preferably in team fight heavy maps.