I'm not a professional. But let's dive into hiragana.
You've got your tools in place, you've prepared yourself for a system of writing radically different from any other, and away we go...
Hiragana are the most common and simple characters in written Japanese. I recommend becoming familiar with hiragana before you begin learning words/phrases/expressions/etc. I have tried to explain to many a beginning Japanese language student that learning the romanized (romaji) spelling of Japanese words is detrimental to your overall progress, but, alas, not many of them were willing to give up the roman alphabet. "It's easier," they say. You might as well make up your own system for reading music. Instead of reading musical notes on a standard musical scale, you could replace the notes with the letters "a, b, c, d, e, f, g" that we use to talk about those notes. You could learn to read music with the notes replaced by written letters in straight-line sentence format, and you might be able to play any piece of music very well like this. However, the day someone puts a genuine musical piece in front of you (scale, staff, and notes) you will be useless at reading it.
This is exactly like learning Japanese with a romanized alphabet instead of kana. The musical piece that is the Japanese language wasn't written in the Western alphabet. This beautiful language didn't pause for a second thinking about how best to bridge the gap between the East and the West. Keep this in mind when you are trying to learn Japanese: it is not the responsibility of Japanese to cross the bridge and render itself in the roman alphabet so you can understand it more easily; it is your job to cross the bridge from West to East using your native alphabet as a starting place and leaving it behind as quickly as possible.
Wikipedia has an excellent yet concise history of hiragana. Read it for fun.
From the Wikipedia chart, there are 41 essential hiragana for you to learn. Just like learning the English alphabet, this is a process you can knock out in a few hours if you just sit down and study. I think it took me a full week to learn all of them because I was a very lazy student in the beginning. My example shows that you can either be dedicated and knock it out quickly, or you can sit around and be lazy and learn 5 at a time. It's probably best if you just knock out the hiragana quickly.
Some great online tools for studying hiragana are:
TheJapanesePage.com This is a nice little flashcard-style learning tool. It just displays random hiragana from sets that you choose.
Hiragana Screen Saver Shows random hiragana as a screen saver for the windows desktop.
Genki Flash Cards An online study tool for hiragana to be used with the Genki I lesson 1.
Charles Kelly's Online Japanese Language Study Materials A nice hiragana flash-based quiz tool, as well as many other resources you can use at more advanced levels.
Hiragana Flash Card Trainer An application for hiragana training on the Palm OS.
The Kanji Site A fun pop-up window shows all 46 common hiragana and displays the romaji upon mouse-over. Good for just starting to learn hiragana because you can change to romaji to kana instantly over-and-over.
There are many, many more sites out there with valuable tools for learning. I tried to provide a sample of those sites with a variety of interfaces. I will compile a huge list of links in the future and comment on the ones that helped me the most.
Everyone will make mental associations with each hiragana. While these associations are unique for each person - I'd like to point out some of the visually similar hiragana that might trip you up.
NU - NE - WA
ぬ ね わ
These three kana gave me a world of trouble in the beginning. You can see how I have them listed, from left to right, they change by one little detail only. For me, it came down to associating ぬ with いぬ (dog). The kanji kind of looks like a curled up dog to me. ね was locked into my mind after I realized that ね is used kind of like "yup" or "right" or "uh huh" at the end of many sentences. Statistically, I'm not sure which kana appears most often in writing, but I think overall ね is the most frequently used kana in speech. Once you learn Japanese well enough to hold a conversation, you will hear ね so often it makes your ears tired. Everytime you hear someone say it - just visualize it. わ actually has four distinct pen movements - just like an English "W." That might be a weak association for some; I hope it helps someone.
Tsu is probably the most versatile kana because a tsu is necessary any time you have a double consonant sound in Japanese (with the exception of an "nna" sound that I will discuss later). Anytime you see a small tsu (っ) you know to make the very next consonant sound into something like a stutter. Conveying this sound on the internet is next to impossible. I strongly advise you to seek the help of anyone who has been exposed to Japanese for no less than 2 months - they will know how to make this sound for any of the kana consonants (k, s, t, h, b, p, r, n, m, y). When writing Japanese words in the English alphabet (also known as romaji), a small tsu character effects the following change: そか (soka) そっか (sokka). The "k" from the か (ka) character is doubled in romanized spelling and the pronunciation is such that the word almost sounds like two words instead of one: sok-ka. Having a teacher or friend demonstrate this for you (if this is your first encounter with Japanese) will save you a lot of stress trying to perfect the pronunciation on your own.
The other hiragana are, in fact, pretty easy to learn. I haven't known anyone to spend more than a week learning all of them. So I probably shouldn't spend too much time talking about them ^_^ There are other, more worthy pursuits for us to spend our time diving into. Like the all important kanji!!!