Depends on what kind of hybrid we're talking about. For a beast like Viper, I went with Deer like legs and integrated the front claws of a raptor into it trying to mimic the shape, I don't change the whole leg. Just edit the feet a bit to match. Like it's easy enough to make a canines paws into a hoof like shape, Bird feet are the hardest. but mistakes can be hidden by feathers.

uhhh good advice is to always have a reference for what your working with available. and um, doing a couple test drawings. to get a feel of where the ankles would be cause that's where I tend to do all of my hybridization in the animal is around the ankle and foot.

Idk if this helps at all.

I have the opposite (hoofed front legs and paws on the back), but it uses the same base method. Here's a very basic hybrid with deer back legs and wolf front legs:

First I started with a basic deer skeleton (traced from an anatomy drawing from google).
Referencing from photographs or scientific drawings of skeletons of the animals you're looking to mix is your best bet in figuring out how to put them together convincingly

Then I applied the wolf front legs' skeleton (note the difference in anatomy/bone lengths and position) and fleshed it out with references:

This is far from perfect but hopefully it can help, obviously you can apply the same method with all different kinds of animals you're trying to mix, and sometimes you will need to get more creative. One such example would be adding bird feet to your front legs, as birds obviously don't have front legs, in that instance you will need to follow Viral's suggestion and just connect them at the wrist (yellow points on my deer skeleton and green points on my hybrid. heck, should have used the same colours for both >:/).

I also tend to drop the shoulder blade down, making a sloped back. I'll draw a visual when I get home from work and drop it here.