Square your fabric after washing. Press so it is flat. Mark an exact 45 degree line from one corner to the opposite side. Mark a parallel line the width of the tape you want, and cut out. Keep cutting additional sections and piece them together at the ends until you have the length you require.
I hope this isn't too confusing.

Bias tape? I have a little bias tape maker. Like Sandy suggests, cut your material on the bias, 45 degree angle, and then you can pull through one of these little tools followed by the iron. Works great.

Sounds cool, bias tape is getting rather expensive. Thanks, hugs, Marji

Here Monica...

So easy to make your own--I've got these in several sizes--many how tos on youtube--just type in bias tape maker.