There are some essential things you should remember whenever you are going hitchhiking. The Hitchhikers' Guide to Hitchhiking suggest you keep these in mind when strating your carreer as an enthusiastic thumber:
Take the most used route
The shortest is not the best in all the cases. If there is no traffic, there are no rides to share. (Think where the trucks are going: industrial areas, etc.)
Carry a good map
You want to know were you are going. It also helps if gas stations are marked, and you don't need city maps. The Shell Euroatlas is quite good for Europe, but not easy to find.
Be in a good, safe spot
Be in a place where the cars can see you from distance and stop safely. You don't want to be driven over. This is actually the biggest danger in hitchhiking.
This is the case that the drivers consider as well. Few drivers stop unless it is safe for them. Some do, but you shouldn't count on them, as they are the minority.
Stay positive, smile and laugh
It is easy to become bored or frustrated when waiting for a ride, but remember that a good attitude will help you get rides. Keep your spirits up by singing, laughing and simply smiling. A grumpy hitchhiker may get rides out of sympathy, but a happy hitchhiker will get better rides and go further distances in less time.
Make eye contact with drivers
Hitchhiking means making a connection with a person driving by, convincing him or her to stop. To best do this, make sure drivers can see the 'whites of your eyes'. Remove sunglasses and keep your hat higher on your head. Smile while you look at the oncoming cars. If you are looking a different direction or your head is down it is easy for drivers to pass by without relating to you. If you cannot see the person in the car, just look at the windshield where a face should be. Focus on each car until it passes. If traffic is light, let your gaze follow each car expectantly. If there is too much traffic, pay attention to each nearby car for a moment. The more you do this, the less time you will wait for rides.
'Mark Snyder an his co-workers (1974) found that hitchhikers doubled the number of ride offers by looking drivers stright in the eye. A personal approach, as my panhandler knew, makes one feel less anonymous, more responsible.' (Source: Social Psychology, Myers. p.503 Social Relations)
When in doubt, use a sign
A thumb or hand gesture will work fine for hitchhiking (depending on the region), but if your destination is not apparent or drivers will be turning in multiple directions up ahead use a sign to announce where you want to go. Use cardboard or similar with a thick black marker. Write neatly in big, block letters.
Say no, if you don't feel safe
Trust your instinct, when it says no. This doesn't happen often, though. Minimizing risk is not being pussy, it's being smart. If you don't feel comfortable with someone, just don't ask him/her, there will be enough other cars.
Be prepared to camp
On longer hitchhiking trips you may need to camp along the way, if you did not receive a ride to your intended destination. Sometimes you can find a hostel or local host for the night, but just in case: bring a sleeping bag and tarp or tent with you. Make sure to bring clothes that will suit you for night weather.
It is also a good idea to check out Hospitality Club. There are many hitchhikers and it's easy to find a couple of places to stay on a long trip.
Use buses and trains
It's not worth trying to hitchhike at all costs. Sometimes it's just more convenient to take a bus to get to a highway or to your final destinations. This is the case especially when leaving or arriving at big cities.