Taking the lane is harder if you're moving a lot slower than traffic (eg. uphill), and is less popular if traffic has a hard time passing you. In that case it might be good to check if you have other options, other roads you can take. If you have to ride on a narrow road, you can make it easier on everyone by moving more to the side and waving traffic past when it's safe for *you*, and signalling and taking the lane again when you need to.

If the road is wide or has several lanes - take the right-hand wheel track and stick to it. You then should have about a metre on your right that's all yours if someone passes you too closely. Watch out for the ones that will pass you as fast as possible (after all you're only a cyclist... ), and then suddenly find out that there's a red light or pile-up ahead and start braking.

I got asked that about the left-turn lane too... waiting for a green, by a seriously grumpy bus-driver, who wasn't even going that way... I answered truthfully "because I'm turning left." He harrumphed, grumbled that I should be following the pedestrian crossing, and closed his window again before I could answer

Good luck with your clueless drivers!