I use a standard 6x24 inch ruler that is marked with 45 degree lines, both ways, and the cutting mat to align the edges. Then it is a matter of aligning, double checking the edges are straight with the lines on the mat, double checking the lines on the mat, laying the 45 degree ruler on the 45 degree marking on the mat, thinking again to be sure you are cutting the angles the right way (ask how I know) and then doing it. I have found that ironing freezer paper to the border keeps it stable and true. I have had few problems since I learned to put the freezer paper on. Keeps it from going haywire. Just do a small piece to feel it out like around a table runner, etc. Always add to the length of the border the amount of the width because you will need that much extension past the quilt top to allow for the angle (ask how I know that!). Double check and it should go together without a hitch. Good luck! Oh, and if there are say three or four strips to go together, I do the strip piecing first. One pattern that I made had me mitering each corner individually and that was a disaster, for me. After that, I learned to just sew them up together and then treat as one. Made life much simpler for me.

Most times the only tool that is needed is the brain and we all have one. I go straight to a video and I also just fold it the way I want it to look on scrap fabric. Most people have the tools they need nearby with in arms reach.