One’s tense will vary depending on what one is trying to convey within their paper or section of their paper. For example, the tense may change between the methods section and the discussion section.

Making sure that the verb is in the same tense all the way through a document or a letter or an email. If you read it to yourself afterwards you'd realise that it was in the wrong tense because we ...

I walked to the shop. However, not all past tenses are written like this as there are exceptions which need to be learned separately. For example: I bent down to pick up a penny. The correct past ...