Hi bkimble,
There are many things you can do to improve your punching power. Here are some suggestions...

1) First and foremost, master the proper body mechanics of the punches you want to improve upon. Having impeccable form is the foundation upon which functional power is built on. With that, find a good coach and have him teach you the proper form, the proper body mechanics. To see what I'm talking about in the written word, check out "The straight right hand" thread on page two of this forum. You can also supplement this with boxing instructional videos. Go to the Title, Ringside, and Everlast websites to check out what they have available.

2) Once you have learned and ingrained the proper body mechanics, apply the law of specificity and start punching the heavy bag with power in mind. Start off by concentrating on single shots. Isolate each punch (i.e. left jab, straight right, left hook, right hook, left uppercut, right uppercut, and overhand right) and do lots of single shot repetitions with impeccable form and violent intent. There are many training schemes you can use, but suffice it to say for now, just put in the "flight time" and do your reps in a strict, disciplined, and an "each shot stands on its own" manner. In the beginning, I'd say do at least 20-30 reps of each punch in varying rep and set schemes.

When you are doing single punch power training, don't just mindlessly and quickly bang out the reps. Do each one as if it were your last, meaning execute each one with purpose and commitment. Again, especially in the beginning, I'd suggest doing at least 20-30 reps of each punch in varying rep and set schemes. If limited training time is a concern, focus on two punches per workout.

After spending an ample amount of time drilling single shots for power, expand your power training regime and start doing double shots (i.e. one-twos, two-punch combos). Some tried-and-true two-punch combos you can work on in this area are: the ol' one-two>left jab-straight right hand, left jab-overhand right, straight right hand-left jab, left hook-straight right hand, straight right hand-left hook, left hook-right hook, right hook-left hook, left hook-right uppercut, and right uppercut-left hook. These are but a few; you can generally put together any two punches together in a two-punch combo. Play around with the punches and find out what "fits" you. Oh, another thing, vary the rhythm used. There are two basic rhythms associated with two-punch combos; they are "1,2" (i,e. bang, bang) and "1-2" (i.e. bang and bang). In both cases, for power's sake, execute both punches with as much force as possible. In terms of rep schemes and such, I recommend the same as above, at least 20 focused reps of each two-punch combo you desire to work on.

Single-punch and double-punch power-focused training on the heavy bag are, in my opinion, the two best ways to isolate and specifically improve your punching power. Along these lines, if possible, use heavy bags of differing weights and densities to vary the contact and resistance feel. Now, if you want or can have only one heavy bag, I'd recommend a firm one that weighs in the vicinity of 80 to 100 lbs.

3) An excellent supplemental exercise you can use is "punch isometrics." Take any punch, let say in this instance, the left hook and place your left fist against a wall in left hook form impact-position and isometrically press the wall in this position for six seconds (exhaling as you do so). The mentality to have while doing this is imagining/visualizing that you are moving the wall. Do this exercise with each punch in your arsenal in at least three different positions (i.e. beginning, middle, end positions). As far as reps are concerned, the minimum is 3 reps in each of the three positions per punch. Be advised, if you have hypertension problems (i.e. high blood pressure) this exercise might be contraindicated for you (i.e. it might not be good for you).

There are various ways to manipulate punch isometrics. You can do them in varying time schemes, rhythms, and positions. Here's one of my favorite methods: one-second isometric bursts done staccato-style (i.e. in rapid succession) for five to 20 reps, doing two to 10 sets. Play around with the concept and I'm sure you'll come up with the different ways.

4) Another excellent supplemental exercise is to use a cable pulley weight stack to perform punch-specific maneuvers in sets/reps. For example, let's take the left hook again; adjust the cable pulley level at shoulder and/or head height, set the weight stack at a weight that gives good resistance but allows the maintenance of good form movement, grab the pulley handle in a vertical fist position, stand in left hook ready position, and throw a fast but controlled left hook with cable pulley in hand for reps (remember to exhale upon exertion). I recommend two to three sets of 8-12 reps for each punch.

Anyway, these are my recommendations. I hope they help you out. Take care...

Best Regards,
Lito