what is the best way to make an electromagnet?

Answer 1

Mike 1942 is almost there. He says use a nail. Most nails are made of steel, this will create a permanent magnet. Most applications for an electro magnet, relays and the like, require it to be a temporary magnet. For this you must use iron.

Answer 2

Buy magnet wire - which is fine copper wire coated with insulating laquer which is very thin - and wind it with even coils around a soft iron core. A heavy nail will serve if nothing better is at hand. The wire must be insulated and the next compromises after the magnet wire are thin cloth and thin plastic - the most common source of the latter being telephone wire. The thicker the insulation, the weaker the magnetic field.