Better Contact Drills
The first thing you need to do is establish what kind of contact you're making now. Just because the ball isn't flying as straight or far as you'd like doesn't necessarily mean you're not catching the ball in the middle of the club face.
Take an ordinary piece of masking tape and put one layer on your 7 iron, 4 iron and driver. (You can pick any clubs, just a good cross section). Don't press down real hard on the tape or you won't be able to see where the ball makes contact!
Make 3 or 4 swings with each club (hitting a ball of course) and see where the pattern on the face predominately is. (middle, heel, toe, high, low) If it's in the middle on all three clubs you can take the tape off and go have a beer. If not we've got some work to do. (then you can go have that beer).
Just FYI, "middle of the club" means about 2 or 3 grooves up on most irons, you can pretty much tell where middle is left and right.
OK, you've determined that you're not hitting the ball in the center of the club face. This explains at least some of your trouble out there. Here are a few drills to try, depending on where on the face you are hitting.
Dimple-Focus Drill (toe or heel shots)
If you're hitting on the toe or the heel, try this "drill". Focus on a dimple on the ball rather than the whole ball. If you're hitting on the toe pick out a dimple on the "outside" of the ball. On the heel pick a dimple out on the "inside"of the ball. Keep your eye on that dimple throughout the swing. (This also helps you make a better shoulder turn resulting in increased power.) The idea isn't to do this forever, but rather to groove the proper swing path so you can slowly focus more and more toward the center of the ball, then eventually the whole ball again.
Feet Together Drill
Another drill you can try is the feet-together drill. This helps your timing and balance. Often when you're miss hitting you are reverse pivoting a bit on the back swing and leaning back on the downswing. This is basically opposite what it should be. This drill can help you feel staying behind the ball on the back swing and shifting without going to far forward on the downswing.
Try a few easy 8 irons at the range with your feet together. Doing this forces you to "wait for it", and will help you get your timing back. (or just get some if you never had timing to begin with.) Try not to lose your balance at the finish. You're not trying for all kinds of distance, just nice solid contact. Do this until you can swing 70% without falling or taking a step
HITTING IT HIGH OR LOW ON THE FACE
You'll read a bunch of drills designed to keep the club on path longer by placing a tee 6 inches in front of the ball, or 6 inches behind, and practice hitting the ball and the tee. I don't like either to be honest, certainly not the one with the tee behind the ball. We've got enough trouble just hitting the ball, now we've got to hit 2 things! Don't think so.
Let's do this instead. Get out your favorite pitching club. Mine's the sand wedge. Drop a few balls in the back yard and practice hitting some short chips and Lob Shots making SURE to keep that left wrist FIRM all the way through impact. If you have to put a wrist support band on to do that then go get one. (keep that wrist firm a foot past impact at least.)
Allot of the time the cause of miss hits and lack of distance comes from a inadvertent flipping motion of the left wrist just before impact. (this isn't just a hackers problem, I've gotten into bouts of this myself and I may suck, but I'm no hacker.)
By practicing this move with very short pitches (5 to20 yards) you'll get the feel for it and see how much further the ball jumps off the club when you keep the left wrist firm. If this has been your problem and you didn't realize it, prepare to be amazed. Keep that left wrist solid all the way through impact and you'll start hitting those irons that you "couldn't even feel" hit the club face. SWEET!
When you've got "the feel" of the shot in the backyard then take it right to the driving range. Start off with the short ones again, then progress up through the irons to the driver.
Make a conscience effort to firm that left wrist up at impact and beyond. You'll see an immediate improvement in your contact and distance.