Hammer:
If you are using the hammer, then you'll have the ability to stun monsters when hitting them in the head.
So assuming you are aiming for the head, the hammer's level 2 charge works well against monsters who's heads aren't low to the ground (Because you swing it up.).
The stationary level 3 charge (Frequently called "Superpound".) is a great move for hitting monster heads that are lower to the ground, clearing out minions and just hitting the monster in general because it has a huge hit radius. The downside to that move is, if you are playing the other players, you will launch them quite a ways if you hit them with that same move. So it's not usually recommended with groups of people all muddled together.
The moving level 3 charge attack is hard to master, but is very effective for hitting heads that are higher up, and can hit with allot of power. The most effective way to use that attack is to start it, let yourself swing for awhile, and then press X (Or maybe A? I can't remember.). What this will do, is it will make you finish the spinning attack with a "golf swing", which is the most powerful (Correct me if I'm wrong.) attack the hammer has. That attack doesn't have nearly as big of a hit radius as the superpound, which makes it a more liable option if you are hunting with others.
As for how often you should use them. If you are playing solo, then the superpound will most likely be your best friend, as it's really powerful and easy to use against most monsters. If you are hunting with others, then the level 2 charge will most likely be used more, as well as some of the level 3 golf swing.
All of that said, the most effective way to inflict damage on monsters is to use your X combo attack, as that is two decently powerful attacks, followed by the golf swing attack. Then press the R button to do a level 1 charge attack, and then start pressing the X button again. That combo is an infinity combo, which is a combo that can repeated without having to wait for a move to end.
So probably the most effective way to use the hammer (In short) is to use charges when the monster is attacking, and use your X attack combo when there is an opening.
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Lance
Since you are just starting out, then guard lancing is probably the easiest and most effective method of lancing for you right now.
Evade lancing requires not only the evasion skill, but a good amount of knowledge of the monster you are fighting so you know when to evade.
Whereas guard lancing mainly only requires the guard skill, which makes it easier when fighting new monsters who's attack patterns you may not know.