Writing. Writing forces you to actually see how each character is constructed, and helps to develop the brain muscles you need to recognize components. Practice each character over and over, filling an entire page. Pay attention to stroke order and proportions. Do it for each character you learn.
For me, I memorize their similarities. For example, 燐、隣、麟、and 鱗 all look similar, and they all share the pronunciation of りん. I know how to pronounce the rest just by knowing one. so whenever you see two kanjis which look alike and know the pronunciation of only one of them, it's most likely that the two will be the same. (Sorry for my bad explanation )
Writing can help I'm sure of it, but I also believe that reading and learning new words can help as much. I never really wrote down any kanji as a matter of fact, just read A LOT. I can differentiate kanji just fine for the most part.
Writing, as others have mentioned already. To add to that, it might be worth getting into 書道, which I recently began doing to help my writing skills.
Also, learning the radicals makes everything easier. Without radicals, it just feels like drawing a random series of lines that somehow make up a character.
And also after you learn enough Kanji, you kinda just get this sense for how a Kanji should be pronounced sometimes just from looking at it (at least, I've had that before), though that's far from all the time. Some similar looking Kanji also share pronunciations, such as 義, 儀, and 議.
If you’re just trying to differentiate between them for now, I would recommend looking into radicals, like ハデクヨン said. Radicals are smaller parts that make up a kanji.
I mainly learn kanji by studying a lot of word for each reading and by drawing a rough "sketch" of its meaning from those word. I don't really bother with the difference first.
After that I try to write them but it takes a lot more time. Also I practice writing the kanji and also words containing that kanji.
I do that once most of them are kinda memorize, then stop studying them for a few months. Then I do a few review to see which one I forgot and after those review, I create a few schedule to work on them (like a schedule on renshuu for the reading that I forgot or a list of words/kanjis on another app to practice writing the kanji that I forgot).
I can also randomly study their etymology, radical, etc on a whim if I feel that it's necessary or just want to.
And it's the combination of all of that that help to memorize them. But the basic idea is don't bother too much at the begining, draw a rough "sketch" (whether it's for the reading, the meaning, radical, or the actual writing part). Doesn't matter also if I only remember the reading or the meaning at the begining. Once you managed to grab a part, the others stuck more easily. It's also not necessary to do everything but the more you look at them from different angle, the easier they become. There are also kanji that are easier than other, so I didn't need to do everything. On the other hand, some were so annoying that I'm still stuck with them today (and currently working on them). I'm also working on them because I have more time to focus on them currently. So yeah, don't need to rush. And don't feel overhelm too if it seems like a lot. I wasn't able to do any of that at the begining. And I still can't do everything at the same time (I just burn out when I try). But with enough time, and stuborness, it works =p And now, I'm hunting down a few of them that have been haunting me almost since I started to learn japanese
Usually writing and studying the radicals helps. Kanji was (and still is) my favorite part of learning Japanese. One way I've been able to memorize them so well was by studying their parts at the highest level that I could understand them.
for example: 桃 / I already know how to write the kanjis 木 and 北 , so I'd only need to remember the placement for each when I'm writing them. I'd also practice writing the kanji by memory during the day by just writing them in the corners of my school papers or something.
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