You don't say what kind of Acer. The RHS gardening book only gives instructions for taking softwood cuttings from Acer cappadocicum, and says nothing about propagating palmatum, which is probably what you have. I think they are usually grown from seed but if you want to try I would take softwood cuttings and give them gentle bottom heat in a humid atmosphere - but don't hold your breath!

Or you could try the sort where you make a small slit in the bark of a young stem - I think you insert something to hold the cut open- and put it in sphagnum moss in a plastic bag hung on the branch- can't remember the name of the process or exactly how to do it but I'm sure somebody on here will be able to tell you.

If the acer has branches low enough to reach the ground you could try layering - again make a slit in the bark and peg the slitted part firmly down under the soil. You can sink a pot of good compost into the ground and peg it into that if you prefer. It will take at least a year to root well enough to move.

I managed a hardwood cutting from a coral palmatum this year. I took about 6 inches of that years growth and dipped it in rooting hormone then planted in sandy soil.

None of the 50 Acer seeds that I planted last October germinated - I scarified some of them but still nothing.