Afaik the only way to get it to look half decent is to start with shaped formed molded carpet panels.
Cut your own car carpet.
A full size van will need more floor mats than a two seat convertible.
Sometimes carpet in a car can get worn or stained and needs replacing.
If you have an usual model of car or if you like to complete projects on your own you can mold the carpet to the vehicle yourself.
The easiest way to complete this task is.
Take out the front car seats.
Start at the front and lay the carpet in the car.
It is not a difficult job if you follow a few basic instructions.
You may need to cut the floor mat shorter on the driver s side to keep from interfering with the operation of the brake gas and clutch pedals.
I have seen 4 maybe 5 attempts at diy cutting stitching car carpet all were miserable failures.
Lay the old carpet on top of the new carpet as a template.
If you re worried about your car floor mats slipping glue shower non slip appliques to their underside.
Cut the new carpet just a little larger than the old one.
Automotive carpet usually is sold based on a specific make and model of vehicle.
Not something diyers are set up to do.