You can wait for him to plant his feet and time his jab, when you start to time that (if he's an orthodox stance), slip your head to your right (away from his jab, not into it) and close the distance with a big step inwards, you can even dig a big right hook/uppercut to the body while doing it. Once you've done that, keep your head in his chest and don't step back out into his range, just work from there. You can double left hook (body/head) or whatever. You can also try to juke him out with in/out, side to side foot work and head feints, get him thinking that you're going to be in his range and let him commit to throwing, then just time the punches he throws (maybe he throws the same couple of punches) and jump in with punches. Just try and mix it up, monotony gets you timed and countered.
