How can I tailor clothing to fit my size?

Marjorie....Just take them up with pins where you need to then hand stitch. Pants are easy at the waist or length but it can get complicated if you aren't sure what you are doing. Good luck

I've lost some weight and my clothes were too large so I just took them in at the seams, following the original lines.

Here's a good guide to tailoring your clothes to fit better: https://www.whowhatwear.com/what-should-get-tailored

Elastic waste bands can be taken up by opening a small spot on the inner fabric near the elastic. Then you can either fold and stitch the elastic or cut it and overlap and stitch (for a flatter spot). Once the elastic is adjusted, close up the small opening with a few stitches

If you work with the seams on the garment, you will have the best fit. I always pin or baste first, before committing to sewing a more permanent seam. Less is better, a little at a time gives you the best fit. Laying a garment flat to compare with one you like the fit on, helps, too.