Set it outdoors out in the open and ladybugs should come to it eventually. Easy. If it's an indoor plant you need to spray them off or remove them with your fingers frequently until the plant gets healthier and the aphids fewer; then you can do it less often.
Not overwatering (keep soil barely moist), a little Worm Gold and avoiding unnatural fertilizers may also help. The potting soil should be bark or peat based, not from forest floor products. If it's not in a pot then humus can loosen the soil when mixed in, or any random organic material on the surface (but not mixed in).
I believe there's a good wiki on how to do this: