Appointment reminders come first for any business that books time, because no shows are a direct revenue loss and the fix is a setting rather than a project. The same applies to booking itself: an exchange of messages proposing times consumes attention on both sides and loses people at the moment they were most motivated. Both are solved by tools you probably already pay for.
Invoicing and payment follow. Recurring invoices should generate themselves, payment reminders should send on a schedule rather than when you remember, and recurring customers should be on automatic payment. Chasing money is the task most damaged by being done inconsistently, because a reminder sent when you happen to notice arrives at a random interval and reads as arbitrary rather than as process.
Data moving between systems is the next category and it is the one that quietly consumes the most hours. Copying enquiries from a form into a spreadsheet, retyping details from an email into your customer records, or reconciling two lists by hand. Most of these can be connected directly, and where they cannot, a general automation tool bridges them. The hours are invisible because each instance is small.
Backups and record keeping should never be manual, because they depend on remembering and remembering fails silently. An automated backup you have tested restoring, transactions arriving automatically from your bank rather than being entered, and receipts captured at the moment of purchase rather than collected later.
What should stay manual is worth naming, because the instinct at this stage is to automate everything. Anything involving judgement about a specific customer, anything where a mistake damages a relationship, and anything you do rarely enough that the setup exceeds the saving. Automated messages that arrive at the wrong moment, or that treat somebody as a segment when they had spoken to you personally, cost more than the time they saved.
Document each automation as you build it, briefly, including what triggers it and where to turn it off. Automated processes fail silently and are discovered weeks later, usually by a customer, and the person diagnosing it may be you a year after you configured it. A line describing what should happen is what makes that a five minute fix rather than an afternoon of working out what was set up and where.