Private Practice is not for everyone, but can complement and enhance ones professional life - even if one has a fairly limited involvement, hence not particularly large income. I can only speak from my personal experience. When I began I benefited from valuable advice from a senior colleague on how to inform GPs in ones locality, how to set fees at appropriate levels and when and how much increases can be made. It is vital to have an efficient secretary to ensure letters and billing is done accurately and promptly. In addition I have always maintained an accurate ledger, in order to deal with ensuring payment of bills owed and owing including tax. A good secretary is invaluable in chasing bad debts effectively but properly. At the beginning I was asked to speak to local GPs on a variety of topics I was interested in, which in the case of Endocrinology is virtually all clinical areas as this is a discipline they often feel quite insecure about. A factor which I believe is likely to grow in providing satisfaction is the frequency that one establishes long standing relationships with complicated patients, seeing the evolution of their condition, when the pressure in NHS practice is for early discharge back to the GP predisposing to delayed re-referral when problems arise. Offhand I can think of cases I have followed for 30 years or more, some providing novel clinical insights as a result.
A final issue is the necessity to provide ready access to oneself in case of urgent need, cover when one is away at meetings abroad or on holiday, and in my case, having relinquished licence to practice, ensuring appropriate handover to a suitable colleague if one cannot comfortably simply discharge back to the GP.