I rarely teach a horse to lounge as I find the point of nagging a horse to go in circles quite... Well pointless. If you're horse "NEEDS" to be lounged before a ride then you're doing something wrong in the saddle, its not that he needs a good 15 minutes running in circles :) Keep this in mind!!!
To properly teach a horse to lounge start him on a lead rope or something about 10 foot long. Lets go to the left/counter clock wise first. Face your horses shoulder with your Left hand on the lead line about 6 inches under his chin. With your Right hand hold the end of your lead rope. Take your LEFT hand and extend your arm pulling him to the left around you, point, ask him to go left/Waaaaaalk (talk to him), point with your hand and your body - while doing this, your RIGHT hand takes the end of the lead and hits/taps his shoulder with it. He should move right around you, keep him going. When he gets around once or twice ask him to whoa. Be verbal, saying "Whoa" and with your Left hand tap, tug, tap the lead.
You can at this time switch him around or keep him going the same way, work him up to moving out the full 10' of this shorter line at a walk.
If you want to change directions, ask him to whoa. Walk up, face his opposite shoulder, take the lead 6" under his chin in your RIGHT hand, point and push him off around you saying waaaaaalk, while your LEFT hand swats his shoulder with the end of the lead.
Don't beat a dead horse with this, once he gets it let him stop. Do a little more tomorrow, in a few days introduce a nice jog. Try moving up to a 20' line in a week or two and getting a working trot. Keep his lessons short and sweet.
Is he bucking under saddle? Does he do this at the walk, trot or canter? Get him loose and soft at a walk by flexing while moving. Light rein, easy bit, use your seat and leg aid to move him more than your hands. Get him to do a circle here, figure eight there, S patterns down a line (swerve left, right, left, right in a slow easy flowing pattern) go around this tree, that rock, turn here, more S pattern etc. You want his head to remain naturally low (NOT a forced arena head set) and you want to get him to where you think "lets go left" and he starts going left. Get him in tune to you and YOU get in tune to him. Make sure he looks happy, he isn't mouthing the bit, when he stops hes relaxed, ears are forward, no tail swishing. Don't just do boring strait lines to the flexing as explained above, walk over poles, weave the pole bending pattern... Do this at a walk until your in tune with each other (a week or two or more if need be) and if you can do this bareback in a halter, even better.
Then move the same technique up to a jog, then a trot, then a canter. He cannot buck, its physically impossible, if he is soft, smooth and HAPPY. Its YOUR job to get him there and its YOUR job to understand him and its 99.5% of the time YOUR fault if hes bucking :)