I don't bother.
I'm only partially joking. I stay fairly current simply because I do this full time and have a wide variety of clients as well as teach a few ground schools per year. I'm always reviewing material for private, instrument, aircraft systems, ground school, etc.
However, I don't bother to refresh myself on minutia. That's what POHs and FAR/AIMs are for. I'm not going to waste my time memorizing pointless details that I'll have to look up again later anyway. We have reference books and kneeboard cheat sheets for a reason.
Even so, I know the feeling of feeling "stale." I haven't taken a checkride since my MEI ride more than two years ago and my last "real" checkride was six months before that (multi commercial add-on). I feel like I need a challenge.
That's why I decided to save up my pennies and do my ATP next fall. Then I'll probably wait a year or two and do my glider commercial add-on. After that I'll wait a while and tack on my CFI-G. Then of course I could do a seaplane add-on. After that...hmm...I'll cross that bridge when I come to it.
Along the same lines, but a much cheaper option, would be to take a CFI ride with the FSDO to renew your certificates every year or two. It's free and even if you fail, that doesn't mean your current certificates get revoked. It just means you have to rent the plane for another hour or two later to retest, or else put up with 16 hours of classroom training through a FIRC
I knew a career CFI and aerobatic pilot who always renewed via checkride. He said he and the FSDO inspector were friends so it was actually fun. Fly around for a while, swap tips, see if they could find a way to stump the other guy, and get a new ticket at the end of the afternoon. Sort of the "ultimate flight review" you might say.