I've always found an easy way to write new jokes is go over old notes. We all have them, or at least you better have. Keep those notebooks once you fill them with ideas and scribblings. I have some that are three decades old and believe it or not there are new jokes inside each of them.
Every time I crack one of the old binders it's like a time capsule of thoughts, a comedy diary sorta. I had this habit of dating stuff that I wrote back in the day and so it makes it easier to know where I was (comedy condo, a hotel, comedy club, home) and who I was with when I made some notes or jotted an idea.