this one........... Sewing lined curtains "These are very simple directions to follow, and for a beginner like me they turned out nice. A tip you might want to try while sewing the lining to the left side of the front panel is construct a temporary pleat in the middle of fabric. I held it in place with pins. It helps keeping the lining flat while sewing. Once I did that it was much easier to keep the seams straight."
Finally a simple no-gimmicky curtain tutorial. This even explains how to make sure your sewing machine works after sitting in storage for years. After spending 40 minutes on Pinterest looking for a tutorial that doesn't produce curtains held together with hot glue and staples, I have finally found the answer. Using this now and saving it for later projects.