He's not leaning forward he's leaning to the left or backward.
Draw a line from the center of his chest to the center of his groin. You will see that line goes to the left if you follow it from the bottom.
Getting the right posture is not easy unless you are lucky enough to find reference with the exact look you want, or you have the resources to hire a model.
The key is to start with lines, make a line for the torse, the arms, the legs and you can get a feel for what the posture will look like and how balanced it will be.
If the pose doesn't look right then change it or just start over completely. No shame in that. It takes me like 10 tries to get the right pose, just with stick figures.
Then flesh out the shape with volume.
If it still looks promising go ahead and add some more realism. I do this on different layers so I can discard the previous layers which are usually messy.
And here's about where I would start rendering.