Do they have to be made out of jeans? It's a lot of extra work cutting patches from jeans (you have to deconstruct the jeans first), plus the fabric is often tough and therefore tiring to cut through. Jeans quilts end up being very heavy too.
Charity quilts are utility quilts (utility quilts can be pretty!), so there's no need to use cotton thread.
For beginners, the best patterns are probably those that do not require matching of seams. Bricks would be one. Cut rectangles of fabric, sew them together end-to-end. Rows are arranged so that the joined bricks of one row are in the middle of the bricks of the upper row.