Pay special attention to which player (or Shakalaka) the monster is focused on. Most monsters will walk up to their current target slightly before throwing out an attack (unless it dash attacks). When you see that a monster turns to a hunter, and is a decent range away, you can run up parallel to where a monster is going to stop for an attack, and start your charge.
Another way to get some good charge hits is that when you fight any monsters who have a dash attack, and you know that all of its targets are behind it after it dashes, it will always have to turn around to focus on another player or you. This is a great time to run up behind it and start your charge, because it takes a few moments for the monster to turn around, so when it does, it gets a face full of white hot GS.
Once you start to understand the move set of the monsters you fight, you'll be able to predict where they go, and punish with some well timed full-charge swings. Then you will be rewarded with one of the most satisfying feelings in the game.
Keep in mind that when you hold dash, your sheathed X button charge-attack has a faster starting animation then an unsheathed X charge.
How do I get information in there? Also, does it have like a screen shot of the monsters? I'm finding it difficult to remember what the monsters names are, and thus have to rely on Google image search (Hunter noob fail).