In addition to books I use Wikipedia and Wikitravel.org to read about the places I am travelling to.
Laws and culture
Remember to respect the customs and laws in the country you are visiting. Things you are used to do back home may be illegal or people may be offended by the way you behave. I.E. in muslim countries one of the worst thing you can do is to touch someone with your left hand or show them your shoe sole. Some places you may get arrested for showing affection in public.
If you get caught doing something illegal you may find yourself all alone and an embassy unwilling to help because you should know what you did isillegal. Read this and this article in Aftenposten about the subject.
Where am I going to sleep?
To most people the choice is either to sleep in a hotel or in a hostel. If you travel alone I recommend you to sleep in a hostel. I have met people traveling alone who slept in hotels. They have described those days as the most lonely days they have had on their holidays. Staying in a hostel you will meet a lot of interesting people from all over the globe. The comfort is better in hotels and you will get more privacy but it is verry likely you will feel lonely if you are traveling alone.
During my travel in Spain in 2008 I had only booked two nights in Valencia. Before I went to bed the secound night I tried to book one more night but because of a concert that night everything was full. I simply had to get out of town the next day. I traveled to Madrid where I had a nice stay. To avoid incidents like mine you should book a few days ahead to be sure you have somewhere to sleep. Book three days in advance and you should be fine in most cases. Be aware that if you are going somewhere and there is a big social event, such as a soccer game, bank hollidays, it may be more difficoult to book places in short notice.
Phone and internet
If you are staying for long in a country I advise you to get a telephone card. Normally this is a much cheaper option than using your cell phone. The telephone operator I am using offer the possibility to send SMS and MMS from their webpage for free.
Most hostels and hotels have internet available for their guests where you may send email, use facebook and other online facilities. Use internett to book hostels (hostelworld.com is the biggest site for booking hostels) or hotels (booking.com or hotell.com are the biggest sites for hotel booking). Booking on the internet you may compare prizes and view feedback from other guests. Online booking sites sends you writen confirmation as documentation. I always prefer to have writen confirmation on the places I am booking.
ebookers.com is a great all-in-one-site for booking cars, hotels etc on the same place.
Equipment
I advise you to purchase a money belt where you keep a backup-card (Visa, Mastercard etc), money and other things you dont have to keep in your pockets. Have nothing more than
a daily consumption of money in your pockets. By doing this you dont loose all your money if you are beeing robbed. By storing money in your money belt you may have some backup in case something happens.
Personaly I prefer using a rucksack while traveling abroad because it makes me more mobile. If you use a wheeled bag or suitcase its harder to drag your luggage along. If you are traveling from city to city a rucksack with a 40 liter capacity should be sufficient. In most big cities it it's quite easy to find somewhere to do your laundry. The disadvantage of traveling with a rucksack that small is the lack of space if you have planned to do alot of shopping. If you have planned to travel in more remote places a larger rucksack is recommended - 80 liters or more.
Buy everything you need in advance. Nomaden is a great place to check out to buy stuff you need. That place has a huge section of map in addition to a huge section of books and other equipment. The advantage of buyinig stuff at a place like this that everything is compact and does not use unnecessary space in your rucksack (or suitcase). On their homepage Nomaden has lists of what you should pack wherever you are going to travel. Spend a few days to pack. By doing this the chance is bigger that you dont forget anything. If you are unsure on what kind of power adapter you need in the country you travel to check this page.
Think twice before you buy souvenirs. Souvenirs may look nice on a holiday may be equivalent to garbage when you get home.
If you are going to use a rucksack I recommend you to use a safety net. The safety net is available in several sizes. Using one of these you are sure that noone will slash open your rucksack to steal things. Because of it's construction you may lock your rucksack to i.e. a pole or your bed. Using this while sleeping at a hostel you are guaranteed that no one will steal your rucksack (or something from it) during the daytime while you are out or while sleeping.
Water and food
If you are going to drink tap water I recommend you to buy a water filter or water treatment tablets. Water is quite cheap in the supermarket and a good alternative to tap water which in some countries may give you problems.
Normally you dont encounter any problems eating foreign food. If you are travelling to another part of the planet be sure to eat food that is properly cooked to avoid any problems.
Dictionaries and language barriers
If you are not fluent in the language they are talking where you are planning to spend your holiday I advise you to buy a dictionary. You will be surprised how poorly people speak i.e English in places you would expect them to be good. If you are fluent in English, French, Spanish and Portuguese you are likely to get along fine most places. Dictionaries come in most sizes, analog as well as digital. It is possible to install dictionaries on your most telephones. I have used dictionaries from SlovoEd and they work just fine. SlovoEd got 130 dictionaries in 30 languages.
Guiding
If you are planning to attend to a guided tour you got three options. You may either (mis)use some locals you know, you may use a bus-sightseeing or you could attend a walking tour. Cycling tour
is an alternative to walking tour in my opinion. A fifth alternative is to walk around by yourself but doing this you may miss the nice spots. (Most people working at hotels or hostels are likely to show on a map what to se though). Use one of the other options first and then walk around by yourself and explore the places you want to explore more by yourself.
The tickets you get on a bus-sightseeing normally lasts for 24 hours and let you hop on and off at any location along the route. Personally I prefer the walking tours because it lets you get close and personal with the cities you visit. In adition to this the guides often tell you things noone else have told you. SANDEMANs NEW Europe Tours offer free tours in several cities in Europe and is highly recommmended.
Medicine
If you use medicine bring it in its original packaging. Othervice you may find youself some trouble in the customs. If the medicine contain something that may be illegal in the country you are visiting bring a letter from your doctor to avoid any problems.
Visa
As a gereral rule you need a Visa visiting another country. You should check what kind of vis you need to avoid surprises at the border. There are several types of visas which you may read about here.