It's a big job praying three times a day. Do what you can to make that job a little easier.
I use these plastic removable stick-on tabs in my prayer books. My dad does, too.
(Actually, I think we did this independently.)
The psalms that I say frequently are marked. In some of my prayer books, all of the kaddishes are marked.
I keep my own prayer book in my shul with all the tabs. And the prayer books I travel with are also heavily tabbed.
Whatever it takes to get the job done. There's a lot to do, and who has time to fumble around looking for the right page?
Note that all but one of the pictured books is Nusach Ha'Ari and one is Nusach Ashkenaz. I travel with one of each - I never know where I'll need to find my next minyan. I'd better be able to find the kaddishes quickly as well. And I want to mark who says what kaddish and when they say it.