Time tracking is the foundation even for firms that bill by fixed fee, and this is the piece most often resisted. The purpose is not the invoice, it is knowing what work costs you. Firms pricing on estimate routinely discover that a category of work they considered profitable consumes twice the hours assumed, and that is invisible without a record. Tracking needs to be fast enough that it happens contemporaneously, because reconstructed time is systematically wrong in the direction of undercounting.
Client and matter records are the second requirement, and the distinction from a general customer database is that the unit of work is the engagement rather than the person. You need to see what is open, what stage each is at, what was agreed, and what happens next, without opening five places. For a small firm this can be simple, and it needs to be one place rather than a folder structure plus an inbox plus somebody's memory.
Document handling in this sector carries confidentiality obligations that are frequently professional rather than merely commercial. Access control, secure sharing with clients rather than email attachments, and a retention policy matching whatever your profession requires are the specific requirements. Sending confidential material as an unprotected attachment is the ordinary practice that most deserves changing.
Engagement letters and scope documentation prevent the dispute that actually happens in professional services, which is not about quality but about what was included. A clear statement of scope, what falls outside it, and what happens when a client asks for more, sent before work begins, resolves nearly all of it. This is the same discipline as any project work and it is applied less consistently in professional firms than elsewhere.
Billing should be regular rather than at completion wherever the engagement allows. Monthly billing on work in progress smooths cash and surfaces disagreements about scope while they are small. A firm that bills once at the end of a six month engagement has funded that work itself and will discover any dispute at the largest possible scale.
Conflict checking becomes necessary earlier than most small firms expect, and it depends entirely on having a searchable record of everybody you have acted for and against. In a firm of one this feels unnecessary until the moment a prospective engagement arrives that you cannot accept, and reconstructing the history from memory and email is both slow and unreliable. A simple searchable list from the first client costs nothing and is the record you will need.