I'm not really sure where I came across this little trick, so I can't give credit, but I thought I'd share it with you. It completely eliminates the step where you mark your stitching line across your small blocks. (Tutorial for the Siggy Block here.) It works beautifully.
The first thing you need to do is mark a line that is parallel to your needle. I use painter's tape because it doesn't leave sticky residue on my machine. Make your tape line all the way to the edge of your machine and make sure the edge comes striaght out from the needle.
Once you have your reference line, grab your fabric, already pinned and ready to sew. Line the starting point up with your needle and line the ending point up with your marked tape line.
Now, start to sew across your square. As you go, keep the end point lined up with the tape line. You should end up with a perfectly straight line across your square, but without having to take time to mark them!