E.Honda is both an easy and hard character to play as in Street Fighter IV.
He's easy because he has no tricky combos to learn, no complex moves to pull off and his basic strategy is fairly easy to figure out.
However, it can be tough working out what to do in each match-up as E.Honda struggles against certain characters, particularly those with projectiles.
Hundred Hand Slap (mash P)
Not as useful as in previous games, because E.Honda doesn't move forward unless you're doing the EX version, which uses up valuable meter. It's worth learning how to combo into it though - you can connect a HK after you hit someone with his Hundred Hand Slaps, so it's fairly chunky damage for not too much effort.
Sumo Headbutt (charge back, towards + P)
His trademark move. Most characters struggle to punish the LP Headbutt without a Super or Ultra (Guile can't punish it at all), so it's definitely abusable against new players. EX Headbutt is worth its weight in gold - it is E.Honda's mostly reliable anti-air and this is where most of your meter will be spent during the fight.
Sumo Splash (charge down, up + K)
Honda flies up into the air, then crashes down butt first. This hits as an overhead, so has to be blocked high. It's fairly hard for players to punish this when blocked. The only danger is if you miss the move altogether, which gives the opponent ample time to do whatever he wants to Honda while he recovers. The EX Butt Splash is great as an anti-air, especially if someone is jumping past you for a cross-up attempt.
Oicho Throw (half-circle back + P)
Honda's throw has pretty good range, while the EX version gets an even bigger boost to its range. Get your opponent to block by hitting him with a crouching jab or similar quick strike, then go straight into the throw.
Super Killer Head Ram (back, towards, back, towards + P)
Hard to land but does surprising amount of damage. You can cancel it off a normal Headbutt (back, towards + P, back, towards + P) so try a normal Headbutt cancelled into the Super against jumping opponents.
Ultimate Killer Head Ram (back, towards, back, towards + PPP)
It has a slow start-up time, so the easiest way to land this is from a Focus Attack crumple. Just charge back while building up your Focus Attack, dash forward once your opponent is crumpled and quickly press back, towards + PPP. Tricky but definitely worth learning.
Basic Combo: cr.MK xx Headbutt
Advanced Combo: EX Hundred Hand Slap > cr.LP xx Hundred Hand Slap