once you've got a good grip on hiragana and the Japanese syllabary you'll have something to map the katakana to, the goal is always to minimize the amount of thinking you need to do--as you've probably noticed, reading is most rewarding when it's effortless--so practicing sightreading is important.
Start with flashcards and anki, first with individual characters and then vocabulary in kana, to get you used to seeing common words and recognizing them by shape (as we do when we read English). Make sure you understand the diacritics like " and °, which modify sounds. Make cards with pairs that look similar like あ・め、わ・れ・ね、る・ろ、き・さ、and は・ほ, so you can train to recognize those details and avoid misreading them when scanning.
Then introduce katakana, keep doing the flash cards, and now when you see a character, you should write first the character you see and say it out loud three times, then write it using the other kana syllabary. Do the same thing for words. Start with simple words with just 1 or 2 mora (characters), then get more complex.
ろ・ろ・ろ・ロ・ロ・ロ
ろく・ロク
へんろ・へんろ
ろんぶん・ロンブン
ろっぽんぎ・ロッポンギ
ロマンチク・ろまんち
ロケット・ろけっと
Don't forget the sounds that require a half-sized modifier, like みゃ、りゅ、しょ, and there are also sounds that you'll only see in sound effects or foreign loan words, like ディ、ファ、and ヴィ. Find vocabulary words that use all these sounds, so you can get used to seeing them being used.
Hard mode for katakana is to write a sentence in english or spanish and then try to write it phonetically in katakana. I don't really recommend this for hiragana, in order to reinforce the mental connection of katakana==foreign words/sounds.
Use your phone and try to use the tenkey/swipe japanese input as much as possible, to get yourself used to thinking of the sounds as grouped by their lead consonant. Then, use the flash cards again and instead of writing it by hand, write a note (or a weird text message) with your phone so when you think of the sound you know exactly where to swipe to write it out.
I also recommend doing a short intense study session RIGHT before bed and within 30 minutes of getting up in the morning. This helps store the new knowledge in your long-term memory. When I was first learning kana, my pace was to tackle one "set" per night, like
あ・い・う・え・お
か・き・く・け・こ
ま・み・む・め・も
and if you can, revisit the characters you've already done and PRACTICE them. The more exposure you get to them (and practice writing), the better.
Lastly, the particle pronounced "wa," marking the subject of a sentence, is always written は. There is no particle written with わ, so if you do see it it's part of a noun or name. Once you start building your vocabulary, you can start learning the particles that help you map out sentences.
