Read your owner's manual and only get what they suggest for regular maintenance.

Find an online forum your car - make, model AND YEAR - and read what folks say!

This was critical for me when I bought Carmine, the Prius, 3 years back. (Wow, 3 YEARS already!) Back then even Toyota dealers didn't know all the ins and outs, and would try to sell you stuff you just plain didn't need - the Prius didn't HAVE that part!

Changing the cabin filter on the Prius is a 10 minute job, I do that myself. Haven't actually had to CHANGE it yet, I annually take it out, hold it under running water to clean it, and put it back. Learned this from the forum, they told us what signs indicate you need a new one vs. cleaning it.

Every time I have my oil changed, the place will put a sticker on my windshield. Each and every one suggests I go back in 6 months of 3000 miles. But the Prius owner's manual is every 6 months or 5000 miles!

You really do have to pay attention, just like reading labels for foods. UGH!

Thank goodness for Prius Chat, or I'd have been done for!