Cavalry is certainly more difficult to use than infantry. Whereas foot troops simply move into position and have all the benefits of supporting models, shielding and greater numbers cavalry trade all of this away for mobility and charging bonuses.
The first step is to make sure you are using that mobility. Keep on the move and use your speed to get into the position you want to. Heroic marches will make your men move very fast indeed.
The next is to engage the enemy on your terms, hit them hard where they are weak then back off and do it again. This takes some practice to get the hang of and is twice as difficult to do against experienced players but it does work.
Finally there are horse archers...
With the modifier to shooting when you move its now more tempting to sit still and fire bows. The increased height of a horse can also help sometimes in firing over walls ect depending on LOS.
However you have also paid a lot to make that archer mounted and in the case of rivendel knights probably want to make some charges as well. You need to find the balance of moving, moving while firing, knowing when to back of and shoot as well as when to charge. Only gaming will give you the insight you need for this, so take em out for a spin
Might points are essential for any cavalry contingent as you will need heroic actions to get you out of trouble or to just make sure you're getting your charge bonuses.
In my opinion cavalry are fantastic, I love using them. They are difficult but rewarding. Taking a small cavalry contingent in a predominantly infantry force is a good way to learn how to use them. Taking an entirely cavalry force is very fun but the most effective army should probably retain some boots in the dirt for flexibility.
Could write essays on the subject but thought I'd be concise