Word of mouth is still IMHO the best marketing you can do, that and your appearance and that of your service vehicle. If times are slow what you can do is put door hangers out in a residential neighbourhood offering a free service call (specify dates). Hopefully you will get several scheduled in the same area on the same day to make it pay off.
Marketing to commercial accounts is tougher. Best thing is to approach property managers, realtors etc. and offer your services, tell them what you can do for them and offer a discount for volume.