The best tip I can offer for keeping straight and evenly in the lane; and I think it works well for everyone, is to focus your eyes father ahead in the lane where you want to go. If you look at the lane lines at all, your brain plays a trick and makes you steer toward the line, and then you realize it and steer back, and this winds up making you zig-zag or keep having to steer back to center. It's the same trick you use when you need to avoid hitting something like an object bouncing around at high speed on the road. If you focus on the object, you'll hit it 100% for sure. If you look in a direction which is clear of the object, you'll go there and not hit the object. Again, same but opposite of what they say in baseball ("Keep your eyes on the ball"), when you want to hit the ball. When you come to a curve, keep your eyes out ahead of the car, and your arms will automatically steer to where your eyes are looking.
NOTE: Of course this is all based on assuming that your vehicle does not have a faulty front axle or steering, or worn steering parts. If you let go of the wheel on a straight road, it should gradually meander to the right (or to the left in British countries), as it's designed to drift away from head-on traffic in case you pass out or fall asleep. If the car does not act that way, and if it keeps drifting one way or the other strongly, or if the steering wheel has a lag (doesn't really steer the car tightly), you might need repairs, and it might not be your driving habits at all causing your concerns...
Charles