Quilting question. Please help. Still learning.?

Hi there, I have been quilting for 50 yrs and I cannot even remember how many quilts I have made at this point. I applaud you wanting to branch out and learn new things! You said you have 12" blocks made, so the first thing you need to decide is how big is the finished quilt going to be? King, Queen, wall hanging, etc. Once this is decided, you need to divide the number of blocks into the width and length of your finished project. Let's say you wanted to use your 20 12" squares to make a throw quilt/lap quilt. It would be 4 blocks wide by 5 blocks long...which without borders would be 48" x 60" long. If you are using 100% cotton you can rip your strips instead of cutting them, which is much easier. Once you know your dimensions (48" x 60") then you can decide how much wider and longer you would like your finished quilt to be. Rip/tear your strips from the side of the fabric that will give you the longest strip. Start by cutting as many 12" strips as you will need for the bottom of each block and sew those onto the bottom of each block, adding the top of the next block to the bottom of the border strip. Then lay out the first vertical set of blocks you have sewn together and sew your first long (uncut) border strip (sashing strip) to this set and continue on til you have it done. Hope this helps, don't hesitate to ask more questions. Good luck!