How do you say "no"?

In the past few weeks, I’ve learned I need to say "no" to some work projects and that I need to learn how to do so without messing up my relationships with my clients. At the moment I work freelance and have two long standing regular clients. I also do smaller one off projects for other clients.<br><br>I’ve been struggling to get through everything and realising I need to say "no" to certain requests. Or I should probably stop saying "yes" to everything I guess!!! I really enjoy my work and have a lot of creativity with it and I get a lot of satisfaction from my clients being pleased with my work. I have a full time job too so this is on top of 37.5 hours a week.<br><br>I’ve had a few projects where I’ve had to work late into the night and weekends to complete for one of the two main clients. I’m so frazzled and have had a few sleepless nights and a few times, I have been burnt out and feel on edge. I’m overworked. This was finally pointed out to me by my partner who has been very supportive and while working hard on their job too.<br><br>I need to learn to say "no" to these projects. I’m pretty sure it’s my fault for agreeing to do them in the first place but I’ve struggled. I consider myself quite confident and I can express myself quite well. I just don’t know what to say. How do you say "no" without messing up your relationships with your clients?<br><br>TLDR: I have a second job where I’ve been overworking myself and I need to learn to say "no" to these projects. I’m struggling to work out how to say "no" without messing up my relationships with my clients.