Spread your infantry, put them in loose formation and advance towards enemy. If you have any cavalry, move them behind enemy lines. Keep moving your cav, since artillery is very slow to aim moving targets. Use hit and run tactics, charging artillery with your cavalry whenever possible.

Once your infantry reaches their line, charge (I guess it would be better if you put them out of loose formation before engaging).

Since you already have cavalry behind enemy lines, charge into their back once the melee starts.