We bill both by the hour and using a flat rate.  For estate planning, probating an estate and business creation, we use a flat rate for predictable matters.  Some probate matters are unpredictable, such as a determination of heirs, and we have to billed hourly for those types of cases.  For trademarks, copyrights, contract negotiations, and mediation we use an hourly rate.  I  collect a retainer in advance before beginning any work.  I have had "good friends" fail to pay their legal fees and so now we just won't start work without a retainer.  We bill our clients monthly so they know how much of their retainer is left.