Tyres are the only four contact points from the car to the road so I pay a lot of attention to them. I would not use the tyres till the threads are fully worn off. I am trying to keep to the regular schedule of maintaining the tyre pressure and checking for stuck stones, minor punctures, uneven wear at least once a month and rotation every 10k driven. Tyre cost is nothing compared to the price of your passengers' and your life, so choose a good set suitable for your driving style.