In my opinion it would work best if you lunged in a round pen. Only because it's easier and you don't have to worry about the line pulling on you and you can just concentrate on the horse.
Get a lunge whip, it's not to beat the horse but it's just another training aid. It will encourage the horse to go in a circle. If you have a round pen available place the horse in the pen. If not just place him on your lunge line.
Stand in the middle of wherever your lunging the horse. Never turn you back on the horse while lunging (unless you're turning around and asking the horse to walk towards you) , always face him/her. You should create a triangle with your body. Your lunge whip should be one side of the triangle (towards the butt of the horse) and your other arm (where your holding the lunge line) should be the other side of the triangle. If you need to tap the horse, SOFT, with the lunge line to encourage him to move forward.
You will want to come at the horse like your the boss, if you're just submissive the horse will sense it and take advantage of you. Sometimes if the horse won't move forward or you're asking for him to trot/canter and he won't you will need to use more commands. Start by clucking or kissing and if that doesn't work stop your feet on the ground and act like your going towards her. Once she starts to do what you asked her for you immediately stop and say "good boy or girl". It's a give release thing.
While lunging you want to look for the horse to lower his/her head and start to lick his lips and chew. This is a good thing because he/she is pating attention and is giving into your dominance.