Able Sewing Machine Repairs suggests that all sewing machines and overlockers should be serviced at least every two years whether used or not.
Every year is advisable if the machine is used often.
Preventative maintenance is always better than having to replace parts or worst case, the machine.
Your operators manual will give you information about some maintenance you can do yourself.
Older machines for instance can do with one or two drops of oil in the shuttle area which greatly reduces noise and allows the machine to run more smoothly.
Always use high speed sewing machine oil and only place oil where suggested in the operators manual.
It is important to use good quality needles and thread on your machine. Take care to put the needle in correctly and the machine is threaded properly.
Schmetz needles are used by the trade for good reason and examples of high quality threads are Rassant and Gutterman.