Do you keep your to do list under a certain amount of items to make sure that it is achievable?

Put only the next step in each process on the list – and move lower priority items to a parking lot list (something besides the active one).

I separate my to do list in to three categories one is morning two in afternoon and three is night so I put them in to each category so it easy to achieve

I have two to-do lists.
1)GENERAL LIST I keep this list on the Evernote app (so that I always have it with me on my phone and see it from multiple devices). I jot in it any activity and don't give it a limit.
1)DAILY LIST Every evening I make on a notebook a list of 6 things, taken from the general list, that I decide to do the next day; if I don't complete them, they go on the followind day's list (it's the Ivy Lee method).

There is no limit to the number of items on my list. However the most important thing to do is prioritize. Circle your top three and only do those items until you are complete them. Then review your list and tackle the next three most important items!

I never expect to get everything on my to do list done in a day, so I don’t worry about length as much. For me, it’s more important to have gotten out everything in my mind, clearly noted which are urgent & important (A), important but not urgent (B), and not important (C). I then pick my top 3 As and focus on getting them done, then the rest of the As, then the top Bs, etc.

After making lists for a long time, I notice that my cap is 6. If I have anymore than 6 I will get fewer thingson my list done.