My house is small and I don't have a design wall. I've amazed myself over the years on just how many ways I can put two blocks together incorrectly just by picking them up from next to the sewing machine and turning them under the needle. With block markers I still have the rare issue of doing things wrong but it happens very infrequently now.
I just fold a piece of typing paper into roughly 1" squares, sometimes they are bigger or smaller depending on how many I need and what folds nicely. I safety pin with super tiny cheap pins from the dollar store which have to get replaced fairly often. I pin the markers into the top left quadrant of the blocks because that is what I'm used to, consistency is the big thing. I don't bother trying to keep them from project to project. Oh I thought that had potential but really, who wants to keep track of 90 tiny pieces of crumpled up paper?
I always Letter Across (A, B, C, D) and Number Down (1, 2, 3, 4). If I have a K9 block, I must use dog fabric!
It gets a little more complex with on-point layouts, I number the diagonal rows. I also keep an overall plan/diagram even if not much more than a grid drawn out that shows the layout. I've attached a recent layout to keep me on track and the project with the markers. Turns out that although I did put them together exactly as I had planned, I decided I hated it and had to take it apart again!
Edit: Couldn't find this picture, but I did find the thread I posted it in. The redone top and border treatment is over here,
Needing Help Finding A Quilt Pattern