Very true, Rab.
I had a a piece of metal coming out of my tire, and the only reason I noticed it was lubing my chain and noticing it on the rear tire. It gave me a good excuse to get a set of Pirelli Sport Demons. (BTW, those are really good tires for the Ninja 250 if you care to spend the ~$300 on getting them. The reviews are right — they have a lot more traction than the stock Dunlaps and I’m actually glad I had to replace them to be completely honest.) If I hadn’t have lubed the chain, I wouldn’t have had a clue the tire was bad!
Check that tire pressure as much as you can before riding. Low tire pressure is a major cause of most tire problems, and when you only have two wheels, you want to keep them both working while you’re riding. 28 front / 32 rear is the lowest you should see. Again, measure it cold. The Ninja 250 FAQ website goes into the debate over what pressure to use.
Checking the oil level on the 250 is going to be something new for you. There’s no dipstick, just a little window that gazes into the engine. If you park outside, on a hot day baking in the direct sun it should show a good level. If it’s not baking hot outside, you should see at least some oil, even if it’s below the low line. After you’ve rode a bit and it’s nice and warm, you can check it more accurately. Now, the trick is to look at it while the engine is upright, not on the kickstand. The 08 and newer don’t have a centerstand, so you’re gonna need a stand or a buddy to hold the bike up for you while you look.
Most of this stuff and more is covered on the Ninja 250 FAQ site: http://faq.ninja250.org