A-level: I did not enjoy it at the time when I was that age I found it pretty boring and samey. With hindsight it is quite interesting and I wish I'd paid more attention. If you are quite an academic person with an interest in your subjects at school then it is probably a solid option. If you're more sporty and not too great with homework/actually enjoying the subjects you do I would avoid it.
Beyond A level: You should make your choices regarding subjects with a view to your future. Decide if Psychology is the sort of subject that you are interested in enough to potentially do at university. If you could see yourself doing it at uni, that means it is probably going to be relevant to the degree you end up wanting to do, that doesn't necessarily mean Psychology. If for example you'd be interested in doing primary teaching and ending up as a teacher or social worker then Psychology a level could be a good, relevant option. If you think you might end up wanting to do medicine for example it is still slightly relevant but less so than a science, if you might end up doing engineering then its kind of irrelevant.
At university level the course "Psychology" is a very popular one and often over subscribed making competition fierce.