You mention timing-belt - I would stick to what the manufacturer recomends. A little early is fine but try not to go over the recommend time/mileage
Note: I thought Honda civic had a chain not a belt and the chain was rated for 300,000 miles, i.e. significantly longer than the rest of the car...
regularly change air-filter, maybe every 3k-5k - trivially easy, takes 5 minutes, cost you $10 and improves your mileage/mpg by maybe 10% so easily pays for itself in reduced gas costs.
I've been told that changing oil/oil-filter more often than the maintanace schedule will significantly extend the engine's life, again was recommended every 5k by a mechanic friend, he would also only use semi-synthetic or fully-synthetic oil, but other people reckon good quality mineral oil is fine and synthetic is unnecessary for a car engine.
1) You need to change the brake fluid about every 2 years (based on time not on distance, it gets waterlogged from condensation in the air)
2) Spark plugs - probably good to do these, will help with better combustion and its not a difficult job. Doing these early makes sense if you are a handy person with correct tools. Will improve fuel economy and may restore a few lost ponies as well.
3) worth to drain out the transmission fluid from automatic transmission (you will only get out about 2 quarts of the total 6 quarts that are inside it). Then refill with MUST BE Genuine Honda Auto Transmission Fluid. Personal experience - did this on my Civic, it had a slightly noticeable shudder when shifting gears before, which has now gone away and is nice and smooth. I have read on internet of other people with similar experiences. And yes, the Honda recommendation is only every 60k miles for the first service then moving to 40k miles after that.