For me, I evaluate each bike based on what I intend to do with it. If it's a bike I'm going to flip and its a beater I complete any needed repairs and sell it. If it's a flip bike and it's up around $100 or more, I'll lube the BB and hubs. I make sure the chain is within spec (.6 or less using a CC-2 chain checker). I replace all cables that show rust, fraying or not performing well. I polish the frame and replace any tires that show rot. I only lube heads if they need it.
If it's one I'm going to keep for my own rides, I usually lube during opportunities when I'm making repairs or if I sense it needs lube. Each bike is different and I perform maintenance based on how much I use it. The one item I must have in good shape is the chain. I'm a stickler for assuring my bikes have good chains, almost obsessive about it. I guess its because I destroyed a freewheel on the first Trek 800 I bought when I rode a dilapidated chain. I learned real fast the cost of riding with a worn out or rusted chain.
If I'm using a bike for distance rides, or one of the MTBs I use for MUP riding, I check those out about once every month during riding season. My two Specialized MTBs that I use for mountain bike riding are the top of the heap. They get whatever they want and sometimes what they don't need. I've got a thing about not wanting to break down on a mountain trail. BTW, it's never happened.