Well, Neville as a Herbology professor. Let's see what I can do.
I think he would strive to be like Professor Sprout and Professor Lupin, most likely his two favorite teachers. Both Professors gave him more confidence in his own abilities. He would try to have a fun, hands-on class (wait, he kind of has to ) while still actually teaching.
He would try to make memorable moments in his class to help his students remember what they learned. For example, let's say that James Jr. got bitten by a plant, and while he was swearing Professor Longbottom explained to the class what he did to get bitten. Then later on the test, if he asked what you can do to not be bitten by said plant, all the students would remember that day that James was bitten.
He has to give homework, and he knows that. He would go for the happy medium, though. He would most likely remember that the professors liked to assign homework like that was the only class. Therefore, he wouldn't assign as much homework as the rest of the professors, but he would still require decent-length essays.
I agree with BlackHairedWeasley. Neville isn't naÔve. He would probably try to be very lenient in the beginning, just because he doesn't want to be the mean teacher that no one likes. However, he would see quite quickly that that wouldn't work, and he would crack down on the problems that arose from his experiment. That's basically what teaching is for awhile, an experiment. So, like LunarEclipse said, he's going to know who to trust. It may not make him the fairest teacher of the bunch, but he'll know he's doing the right thing.
Well, there's my two bits. Ta ta for now!