The Overview: Choosing your route, making intelligent signs, taking only useful rides are all easiest with a decent map.
A high detail map which covers the area of your trip is worth the 5 or seven bucks you'll pay at your local book shop. If you don't want to pay for a map - head for a tourist spot: hotel, airport, bus station, tourist information booth - there you can page through the "Visit Manitoba!" type pamphlets for something with a decent map. Rental car places have the best free maps.
In choosing a hitchhiking map, find something which covers your trip and which has road numbers for the roads you'll be traveling. Ideal is a map which also shows rest areas and gas stations - they're good places to grab your next ride.
The premise is this: we don't want to resume hitchhiking where we'll never again get a ride. So, if we catch a decent ride, say someone going a hundred miles in our direction, but their destination, the place where they will leave us is a shit-I'll-have-to-sleep-here-tonight town on the side of the interstate. No on-ramp back onto the interstate, no gas station, no where near anything. With this ride we may, if we consult our trusty map, find that we should take the ride but get dropped off at the Flying J's Truck Stop 30 miles before their destination. (The Flying J's or the rest area along the way.) There we're sure to get another ride. It's easy to hitchhike away from truck stops and rest areas.
The Resolve: Don't get left at an on-ramp for local farming tractors. Get a decent Hitchhiking Map - it gives us foresight.