There is no such thing as a "pure" accent. You can decide to concentrate on British English or on American English, making sure you listen to the relevant pronunciation on sites like Forvo. You can find lots of sites which list the differences in spelling and vocabulary between BrE and AmE.
At your stage, I think it is more important simply to concentrate on learning grammatical English and correctly written English. For example, the word "I" is always capitalised regardless of where it appears in a sentence. We don't put a space before a comma but we do put a space after a comma. We end sentences with a full stop, question mark or exclamation mark and we start every sentence with a capital letter.
Student or Learner