All that is already written here is good advice.
Most important! Have fun
Try to make it fun and interesting, always. Otherwise it just becomes a big chore. Have it relate to the content you dream of consuming when you’re “fluent”. When you’re inventing mnemonics make them silly, gross or offensive. Same with example sentences for learning grammar. A fun and emotionally engaging study session stays in the memory longer than than a boring ass repetitive grind.
Consistency is next most important. Studying Japanese for half an hour every day is more effective than doing six hours at the weekend even though it’s nearly half the total time. Every day puts things into your subconscious mind more quickly. Have you seen the movie The Shawshank Redemption? It has nothing to do with learning Japanese but has a good philosophy/message that can be applied to learning Japanese.
Don’t underestimate the importance of daily listening practice. It helps you to remember readings that are exceptions to the rule and is the single most important factor in being able to hold a conversation.
If at any point you feel really frustrated, that is normal. It’s usually a sign of burnout or a least mental tiredness. Similar to lactic acid in the muscles after exercise. It’s OK to take well earned breaks. Plan rewards for achieving learning goals. For example, once you feel like you know hiragana and katakana like the back of your hand celebrate (go out and get hammered? ) that in style giving yourself a big psychological pat on the back.
Always keep this in mind. I AM NOT STUPID. Japanese can be rather challenging at times.