Learn your kanji!
Kanji is one of three Japanese writing systems along with hiragana and katakana. Both hiragana and katakana are phonetic, meaning that each character represents a single syllable, and that character will never be pronounced any other way. Kanji is a system of symbols that represent words or ideas, and that can have different meanings and pronunciations depending on their context. A kanji can be a word all by itself, like 木 (which means tree) or a kanji can be part of another word like 木造 (which means ‘wooden, or made of wood’).
There are multiple ways to pronounce almost every kanji. These are known as “readings.” There are readings that came from the original Chinese and then readings that came from the original Japanese. The Chinese readings are known as On’Yomi and the Japanese are Kun’Yomi.
There are more than 50 000 (!) kanji in Japanese. Don't panic! Only a few of them are really used. An average Japanese adult know between 2000 and 4000 kanji. However, if you want to understand around 95% of what you read, only 1000 kanji will get you there. 2136 joyo kanji gives you the government mandated minimum literacy and pushes you up over a 99% comprehension rate.
My kanji lists are supposed to be sorted by difficulty (from lower to higher), following the JLPT lists. Every list is made of 50 kanji. To be efficient in your learning, you should try to pronounce them multiple times, while in the same time writing them. Don't forget to respect the stroke order!
Just like with hiragana and katakana, it exists different rules to write kanji.
1. Top to bottom, and left to right
2. Horizontal before vertical
3. Character-spanning strokes last
4. Diagonals right-to-left before diagonals left-to-right
5. Long centre verticals before smaller "wings"
6. Left vertical before across and down
7. Enclosures before contents
8. Dashes come last
I recommand you to read the following article that gives you different examples and exceptions to those rules.
To be honest, you don't need to respect all the rules when writing your kanji, but you should at least follow the 1. and 2. ones if you want your kanji to be well written.