Do you have any genuine tricks for keeping/maintaining a car that are frugal?

Could be anything from getting a deal on a car wash, or keeping the interior nice, or keeping the engine or tires or anything really in good order.

Also, are there any things you used to be able to do frugally with your car which has changed to be more expensive--maybe due to auto manufacturers changing how cars are designed?

(I'm asking this so if something used to be frugal but isn't now, people speak up about it.)