How do I remind myself to run in-flight checklists? When flying a basic light aircraft with no "modern" instrument the pilot needs to remember to do various checks on a regular basis (FREDA every x minutes, change fuel tank every Y minutes etc.).

Just flying the plane can be consuming a lot of attention (especially without auto-pilot or if you become unsure of your position) and it's easy to forget to run those checks. I wouldn't want to forget changing fuel tank so I was wondering:

What are the tools that I can use to make sure that all checks are done on time?
In my view, the best tool for reminding yourself of recurring "household chores" is by using a timer, if the noise profile of your aircraft allows it. (Try it! You can probably hear more than you think, even in a loud prop). Either use a kitchen timer (which has a really simple physical interface, although two hands may be required) or your smartphone (a bit more complex interface, typically allows for single hand usage, with the added benefit that you can run multiple independent timers, and that the alarm will not stop sounding until you dismiss it). Modern GA EFIS (for example G1000) typically have timing facilities built in.

If you are unable to use an actual timer, determine the interval of the task (for example every 15 minutes), and use your normal watch. (For example "Check the tank every time the minute-hand passes the 0, 15, 30, 45 marks").