Hi Sonja - you don’t say what software you use for processing, but an important step to take before any printing, at home or to an outsourced lab, is soft proofing. Lightroom has functionality dedicated to it. Other apps might as well, but I use Lr so it’s the only one I’m familiar with. Basically what you need to do is to ready a photo for printing which is a different media entirely than viewing on a screen. Screens have light behind the photo and paper doesn’t so the qualities of the photo need to be adjusted for that. I find Anthony Morganti’s tutorials valuable, so here’s a link to one that explains this process -
There are more tutorials out there and of course any reputable lab will work with you to proof your images before printing.
Oh and Sean Bagshaw has a whole course dedicated to printing. It’s very technical, but that’s the nature of printing.