First Time Longeing

Be consistent and just push her forward more and say jog, keep saying jog.  I have found  by getting them voice command trained it works so much better for both that go too fast or too slow.
 
 

Body position is important when lounging horses.  If a horse is being lazy, step toward her back end so that you are pushing her forward.  A slight tap or flick of your lounge whip on the hocks or hind end with your whip as you ask her to move forward also can help her associate the voice command with the action you want.
For the horse that goes too fast, take a step toward her front end and use half halts as her inside hind foot hits the ground.  This will signal her to slow it down and the half halts will bring her head down and bowed and force her to work off the hind end giving you greater control.
If I could draw a picture on this thing, I could demonstrate your proper position in regards to the horses you asked about.  If you try it and can't figure out what I mean, I will try to explain it more thoroughly.  Let me know.

I had the worst time getting Zag to circle at one point.  Partly because he HATES it!  But we were at one trainer's and he corrected my body position.  The best thing that helped me, I think was keeping my belt buckle facing just behind the girth.  (even though I wasn't wearing a belt and Zag was bareback.... you get the gist!) []