I've learned spoken languages by writing words down, hearing them and remembering them, and working on websites.
However, I don't see that helping if I learn a sign language. None of those techniques will work. What are some effective ways I can learn a sign language, then?
When I was learning ASL, I found that signing along to tv shows and videos allowed me to develop the muscle memory. Because many words (in ASL) do not have "official" signs for them, practicing fingerspelling of sentences also helped when I needed to spell out words that have no sign associated with them.
Written sign language dictionaries are useful for looking up and practicing words, but because there is no corresponding "written" part to sign languages (whether American, French, Spanish, Chinese, &c.), the suggested practice to drill the words into your mind is through visual/actual practice.
As is often repeated, practice makes perfect. So repeating the different components of the sign (which could be said to constitute its "spelling") and fingerspelling the words followed by the actual sign (for those that have them) is the closest analogue to what you do for other languages.
Additionally, recording yourself on video and watching it again is the visual equivalent of writing the words over and over. It gives you an opportunity to see how you look while signing and if you need to tweek body position, facial expressions, relative distances, and the like. It will help your movements become more fluid, because if you cannot understand yourself after watching your recording, neither will anyone else.
Muscle memory is by far the best way - in that sense, learning ASL is somewhat like learning to play the piano. At first you have to continuously follow the notes, but after a while, the first page of Fur Elise becomes second nature. So, as always with languages, practice makes perfect - you just have to trade in your pen for your fingers in the case of ASL.
For fingerspelling, you can practice in all manner of ways, including choosing a word at random from any book/dictionary, or fingerspelling whole sentences in whatever book or magazine you have open.
For recognition, apart from the obvious choices (course videos, online dictionaries, Switched at Birth episodes, etc), you can also watch ASL interpreters on the news. Whatever you choose to watch, try to focus on the various aspects of ASL - the sign itself, facial expressions, style, etc.
While there aren't many ways to easily write sign languages down, there are also flashcards of various types that you can use as aids - e.g. Barron's 500 Flash Cards of American Sign Language - but just going through the cards without making the accompanying gestures won't help you much.
Finally, while flashcards for recognition must have images (or videos, if we lived in the world of Harry Potter) on them, keep in mind that for recall, you don't need must beyond a list of words. You can probably get away with a stack of cards with the word on one side and a verbal reminder of some sort on the other. If you really don't remember what the sign looks like, you can then check in an online dictionary, but for the most part, this should be sufficient for review purposes.
