I have something so much better, at least in my humble opinion. I use a sheet of lined paper that I tuck under my blank page to create perfectly straight lines that are there. But not. Using a guide sheet does not require any prep time. Just slide the sheet behind your current page and start writing.
Great tip from Ana. But, where does one get such a sheet?
I have created lined paper guides in 6mm, 7mm, 8mm and 10mm spacing. Each .pdf file includes a full 8.5×11 US Letter sized guide and a smaller 5×7? guide that you can trim to fit in the average A5-sized notebook. Print out your favorite line width spacing on a laser or ink jet printer. One copy of the guide sheet can be kept in each of your favorite notebooks and should last for a long time. The guide sheet often doubles as a blotter sheet, pen primer or to protect the next sheet from pesky bleed through.
Boom! Downloadable PDFs. So helpful, that lady.