ive sat 2 MFL gcses in year 10 and im going into year 11 to sit spanish, ill try give you the best advice that i can give :3
essentially the main thing you want to get down is the vocab. it may seem a bit obvious but in the listening exam those spanish people will not only speak at unhuman speeds or have the heaviest accent youve ever heard but they will use synonyms for words in the paper so if you learn your vocab you're all good. get familiar with your specification and the modules (for example one of the igcse edexel modules is house and home, with the submodule being daily routines). once you find these look up the modules on quizlet (i find this to be the most useful) and start revising them.
in terms of speaking, duolingo lessons don't develop speaking skills very well. true, there are speaking exercises integrated into their lessons, but they're just not very good. essentially, you're just asked to repeat words and phrases in a vacuum. it may seem tedious but for your gcse speaking exam you NEED to practice with others, whether its a friend, parent or dog its the best way to practice speaking. for my speaking exam we have to describe whats in a photo and have a conversation with our examiner about 2 randomly selected modules from the specification. this is why learning the vocab is so important, without it you literally have nothing to talk about. with speaking being 25% of your total gcse its rlly important to get a decent grade in it. a 5 in foundation tier is pretty decent and is a good base for higher since theres not much thats different.https://imgur.com/a/1SFX8Fn
<- heres a link to a little screenshot of the speaking section of the spec (gcse edexel, not sure which exam board youre using but it wont be too different)
as you can see, just understanding the vocab will allow you to successfully respond to most of the assessment objectives. then ofc theres grammar and conjugations on top of that but i reccomend building a stong base by learning the vocab and then spending time to learn the tenses (conditional, imperfect, present, future, preterite)https://bassingbournvc.net/wp-content/uploads/2019/09/All-GCSE-tenses.-Regular-verbs.pdf
<- another link to all the tenses you'll need to know to get a 9
finally, dont stress! theres still a few months till your gcses so if you revise well you'll be fine :3https://www.youtube.com/watch?v=5QU1TsOsgqA
<- heres a video for the speaking exam info, i hope this helps too