Hello,
I do French, but I suppose MFL subjects link together in a way?
I would suggest investing in a CGP guide, they include a massive section on grammar, which really helps 😁. I don't know if it's the same in Spanish, but I do AQA and we only have to recognise the subjunctive because it's more for A Levels (unless i have been mislead 😣).
As mentioned, use Seneca, but do not rely on it too much. Duolingo is great for both vocab. and grammar and Memrise is good for vocab. Use Lyrics Training to get used to vocab through songs. If you are really struggling, look on YouTube because there are SO MANY useful videos! 😊
Finally, you might not like this, but write on a table. Literally, buy some felt tips/ markers that rub off and ask a friend/ parent to test you on a tense or a topic. Write down everything you can think of that is relatable (endings etc.) , and afterwards look to see if you got it right. If you haven't, write it on a post-it note and stick it on a wall so that you are constantly looking at it. After you have done, clean the table (obvs. 😂) and start memorising!
Oh, use mindmaps or revision clocks (google if unsure) and on the back, draw pictures/ phrases that help you remember the endings. Create flashcards and use Quizlet for tenses/ irregular verbs. Most importantly though, you have to learn to love the language and have fun with it, because then you'll want to learn it. Listen to music and immerse yourself in it or use social media with it to enjoy yourself.
Eventually, do practice papers to see if you've improved! ☺
Hope this helps and sorry if it doesn't. 😥 Sorry it's soooo long!😯