Hitchhiking might not be so common or the most popular way of travelling distances. However, if you know some rules and tips, it is not as hard as you think and certainly not as dangerous as film industries convince us to believe so. Firstly, know where exactly you need to go and get a good map. Recommended type is not the one you have to unfold every time you use.
A book type is way more convenient and contains more information. You would want at least 1:1,000,000 ratio and better pre-mark important spots such as petrol stations. Once you know the destination, you need to identify the good spot to stand. There has to be decent amount of traffic, ideally the road connecting major cities, but also with an enough space for you and your bag to stay.
The signs need to be clearly written, but it does not always need to say the name of your destination. Some hitchhikers put the road name which seem to work quite well. As cars passing by, have a good eye contact with drivers. I sometimes see ones wearing sunglasses, but I tend not to stop as I cannot see what sort of glance he/she puts under the reflection. Avoid having more than one bag or asking for a ride in a rash hour when people just want to go home. Once you manage to get in, show your gratitude (remember, you are riding FREE) and be a good company for the driver.
Whether you will be the initiator or the listener, good communicator makes the journey comfortable for both and it will not be so long until you reach your destination.