You want new customers, more work, more money. You advertise, you receive phone calls, you meet new people, you give estimates, you sell yourself and your business.
You hope that a certain percentage of those leads turn into paying clients.
This is business.
But once your business is established and you have a client list of people you service regularly or people you have serviced in the past, up-selling will save you a lot of time and potentially make you a lot more money.
These people already know you. They know how you work. They trust you. They like you. They are already spending money with you.
You should constantly keep your eyes open to find new services to sell to your existing clients.
And you should constantly remind your existing clients of all of the services you offer because chances are they are not aware or did not remember.