Once again, I'll have to pit myself against the convention here on the forum. I prefer a chain over a strap ... at least for on road motorist assistance. Straps are better for off road applications tho. With a chain, you can double it back on itself to adjust for length. Many times it's difficult to position the recovery vehicle to use the full length of a strap. Just don't try to snap with a chain like you can do with a strap (snap is only useful if the stuck vehicle is axle deep in gumbo anyway).

As far as where to connect to the stuck vehicle ... GFL. There are precious few points on modern cars. Usually you'll have to get dirty & climb underneath to find anything strong enough like: the frame, the axle, or part of the suspension. Just be careful that whatever you hook to, even if it's strong enough, there may be fragile 'things' around it (such as brake lines or wire harnesses). If you're helping a stranger it's not a bad idea to let them make the connection so that they are responsible for any resulting damages (but be nice & check to make sure they didn't do anything stupid).

Remember also that the best way out is usually the way they went in. If they dropped a wheel or two into a ditch, you'll probably have to come at it at an angle though.

Don't underestimate the usefulness of spotters - just make sure they stand at a safe distance.

If at all possible, drape a blanket over the strap or chain at the 1/2 way point to act as a dead weight if the strap or chain should break.