Try to pick a dark line in the tartan - if relevant, to sew along, and get a thread which is a good match to the colour. Go for a slightly darker shade rather than a lighter one as it will show far less.

A polyester thread is slightly elastic, so less likely to snap if pulled, but can be slippery and move in the seam. I prefer a polyester cotton mix if I can get it. Once sewn it seems to remain where it was put.

Don't be surprised of you quickly aquire quite a number of different spools of sewing thread, plus numerous needles of different types, the 'good' scissors you need for cutting cloth and the snips for the thread, tape measures, hem gauges, boxes of pins, and an amazing amount of other stuff.

My thread collection fills two large tins originally aquired full of chocolates for Christmases past, I have a large plastic tool box plus the boxes for the sewing machine accesories and all the bobbins with thread wound on them.

Once you get over a certain mass I think it acts as a black hole and sucks things in.