Elephants

[Geoffrey S]

Keep them near the battleline for a morale penalty to the enemy, out of range from skirmishers, and never send them in unsupported. Very useful with cavalry or a screen of infantry protecting them.

good but the RTR elephants are better

They are also RTRs elephants, not EBs to use.

[The Errant]

People tend to forget that while they are big and ugly, elephants are still heavy cavalry. They are very weak against javelins and certain types of archers so sending them against either is suicide.
As long as you remember that, using them is easy. Like Cavalry they are at their best when charging from the flanks or back. Attacking a pikeunit from the front is a definite no no.
They aren't as fast as cavalry and should never be used to pursue broken troops. Their advantage is in their mass and ability to frighten infantry. Like heavy cavalry their duty is that of the hammer. Come in from the flank or rear. Charge. And watch the enemy take short leaps in the air only fall and break their necks. If that dosen't brake them, reform and do it again. Some weak melee units they can charge headon. And they can push their way trough pikeunits, but they will take a mauling doing it.
Apart from that, as long as you protect them from enemy skirmishers they can easily win the day. It's just a matter of using them the right way.