Just basic repairs for the most part. I did make a chef's apron and shirt once about 35 years ago for a 4H project. I like building things. Really it isn't a lot different than construction or carpentry if you think about it. Stitches instead of glue. Follow your pattern / plans, think about it logically, where does it go, how is it supposed to fit, do your site lines line up......
The difficult part will be stitching all the pieces together and make sure all the lines intersect where they should, and that it will fit over the seat and look straight in the vehicle. I will have to take a lot of time checking and re- checking my layout before I start stitching.
It also helps understanding the mechanics of the sewing machine itself. Does it want to pull to the left or right. Is it easier to line up the needle on a line, or to offset the line and use the pressure foot as a guide. I found that I can track straighter if I line up on the needle. I found that when trying to follow the line with the side of the pressure foot, my needle tended to wander to the line. On these big panels it is important to hold it as free as possible, make sure you are not holding it back, or force feeding it. Let the machine do the work and just guide it. Support your work, nothing screws up your stitch more than when the heavy fabric is hanging off the table. It is tough to guide and will slip making your stitch length too close together.
And grow longer arms for large stiff pieces like my inserts. I found that I had to sit way back once I got the needle set to support and guide the fabric. I think it also helped for straighter lines as you have a long line to follow or sight down when you are sitting back.
Oh, and after a few stitches and you are halfway through your panel, check your bobbin for thread. It sucks when you run out half way through a stitch line and with the larger diameter thread the small bobbins aren't quite enough to do the whole panel (at least the larger backseat ones).
If any one has any practical tips on making seat covers please share them. I would rather learn by someone else's mistakes than mine. I am still learning and refining my process. Not sure if it is right or not yet.