Many people new to leather work will use "reclaimed" leather, if you're talking about cutting up old couches or jackets or things like that. Choose your worst pieces to practice on - then use your best pieces to make your item.

Most reclaimed leather will have had a finish on it to protect it. That can make it harder to work with. A good cleaning should always be your first step, then condition the leather afterwards to put the good oils you may have taken out during the cleaning back in. Let the cleaned and conditioned leather sit for 24 hours before using it on your project so it dries properly.

If there is still a finish on the leather where you want to sew it together, lightly sand off the area where you are going to glue it, so that it becomes a bit rough and the finish is gone, so that the glue has something to "grab" onto.

My best suggestion for marking on any leather project is to use chalk to make your marks. It disappears easily when you are done or at worst can be removed with a lightly damp cloth without leaving any permanent marks on your finished product.

Feel free to message me with any other questions you might have and I'd be happy to help if I can. :-)