To maintain a proper / manageable coat for non-shedding breeds such as Poodles, Bichons, Shih Tzus, Lhasa Apsos, Terriers, you should have your dog groomed every 4-6 weeks.
If they are kept in a very short cut, these breeds may be able to go 8 weeks before next groom. Breeds that have short, shedding coats can usually wait 8-12weeks between grooming appointments, as long as they are brushed regularly at home.