Since I write out kanji when learning them for the first time, I adopted the Jisho.org format when I’m writing out on’yomi readings in katakana. That helped me a lot with recognition and reading👍
Also, this app helped me to practice it daily: Kana iOS app
Play videogames:
ファイアボール
アイスストーム
サンダーショック
。。。
Whoever it was that came up with the シ、ツ、ン、ソ、Katakana is my mortal enemy…
I mean you’d think artificial alphabet would be simpler when there are so many different shapes that wouldn’t be muddled up.
I think once you conquer those characters, you’ve conquered Katakana. You can remember the rare characters like ヲ by process of elimination I think 
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Okay, I know I already replied with a little rant about the good old quartro シツンソ, but I have some actual advice and that is… Reading!
Don’t obsessively attempt to memerise them, just read through Japanese content and you’ll be getting enough exposure to them that they will just natural float into your long term memory; at least that’s what happened with me.
The only instance of Katakana “wo” I can think of is Zelda for NES. That game is ONLY Katakana 
About the “smileys”, well you’ll get used to them. I read the quattro as shitsunso, so it’s okay
Yeah, I’m fine with them now. I just know how f***ing tedious they can be when you’re learning them. My god, the minutes of brief frustration will never leave my memory. 
I can read them out loud at a good speed, but getting the meaning is sometimes a totally different story You have to actively read them out loud
surprised no one posted this yet
Just as additional information for anyone who’s interested, especially if these katakana are difficult for them: all of these kana except for ン share origin kanji with their hiragana counterparts:
Here’s a related post on the same thread that includes diagrams from Wikipedia on kana origins that might help making the similarities easier to see:
This. After many years I still read katakana much slower than hiragana and I attribute it to my brain trying to map it into words I already know but failing miserably. And yes, I know words like パン and アルバイト don’t come from English, that just makes it that much harder.
I’ve not had much trouble learning, memorizing, and recognizing Katakana. However I find it way, way, way harder to memorize the vocabulary. I think because many of them almost sound like English, but different, and it’s hard to remember how exactly they’re different
When I was learning シ and ツ, my go-to was to inagine two people, Shi and Tsu, holding a shih-tzu between them.
It doesn’t really help with writing, but it did help me recognize them.
Also the anime series ソ・ラ・ノ・ヲ・ト.
I’ve really gotta rewatch that someday.
I know, sometimes I’ll read the word half a dozen times and it still isn’t clear that it’s an English loan word. The pronunciation is just so butchered .
Also ヲタク if you’re legit.
Also ヱヴァンゲリヲン新劇場版 (Don’t ask me why they changed it)
My personal way to remember is a quatro phrase:
ツソシン
つそしん
Down-down-right-right
It’s my katakana Konami code. 
I would second this, especially older games where there aren’t a lot of pixels and you really have to understand the shape.
More examples:
レザーアーマ
トゥハンドソード
シルクローブ silk robe
レベルアップ
スタート
ロード
セーブ
this is really not helpful but shitsu sounds exactly like “poop on” in french (in a vulgar way) and i cannot seem to replace any of the mnemonics with the dog. my brain… my dirty brain made that connection and i can’t fix it 
so your is shi is low and tsu is high or is that by chance in the pic? cause that’s how i do it: tsu is high shi is low.
Mostly, I just place them so that it looks kind of like two people looking at each other; シ looks upwards and to the right, and ツ looks downwards and to the left.
My opinion is that since it’s used less, you get less exposure, hence, less practice and so it is harder.
I used just two resources to learn Katakana very quickly
Tofugu’s Katakana Guide
to learn with mnemonics (Write it down if it doesn’t stick right away)
and
Take this quiz every day or as often as you can. Your first time around, it might take 10-15 minutes to get through all the single and combined Hiragana and Katakana. In a matter of two weeks, I improved my completion time from around 12 minutes to 5 minutes, 39 seconds. There are also other online games that I tried just for some variety, but RealKana is straightforward and will help you learn very quickly. You can also experiment with multiple fonts, which will deepen your understanding of the symbols.