When I think about basic golf equipment I tend to think of the old Jeff Foxwothy stand up routine "You may be a redneck.." except I switch it to "you may be a hacker if..": you've never changed the grips on your clubs, you've never changed the spikes in your shoes, or you don't replace your glove until it rips.  Often the casual golfer ignores these items items because they can't tell a difference.

I tend to change my grips every 40 rounds or two years depending on which comes first.  I prefer to change grips at the beginning of the season so that I start the season with the best possible equipment.  Over time your grips will lose their tackiness to the point that they are hard and slick.  Over time this will lead to the club slipping in your hands and errant golf shots.  Some clubs that I use a lot, like wedges or driver, I've actually worn out the grips faster than others.

When it comes to switching cleats it's not hard to see when they should be replaced.  It you have broken cleats you will be more likely to slip or move your feet during your swing.  Even a slight lose of traction can cause a shot to go errant.  New cleats also provide better cushion for your feet when you walk.  Cleats are fairly cheap so you should change them out often.

Glove wear and tear happens over time.  Often you can play with a severely worn glove but an old grove is like playing with old grips.  You should probably buy a new glove with every other box of balls.  I often keep two or three gloves in my bag in case of rain or a rip.  If you play a glove till it's worthless you never have a backup plus if it starts to rain you can use the old one and avoid ruining a good glove.

My last suggestion on maintenance is to clean the groves on your clubs.  Clean groves will help you spin the ball off your clubs and get better shots.  I'll wash my clubs after a round on occasion to make sure my clubs are clean.  I'll also clean my groves during a round with a tee.