Push the tyre up against the left-hand stay and tighten the (left) nut 75%. The shove the tyre back towards the middle of the stays, and tighten the other nut (with your free hand, obviously). Then make small adjustments as necessary (one side at a time) till it's central and doesn't bind at the tight spot. If you're lucky, it'll be about right first time...
Push the tyre up against the left-hand stay and tighten the (left) nut 75%. The shove the tyre back towards the middle of the stays, and tighten the other nut (with your free hand, obviously). Then make small adjustments as necessary (one side at a time) till it's central and doesn't bind at the tight spot. If you're lucky, it'll be about right first time...
Does that make sense?