As far as using particle correctly, whichever order is fine. The order will be decided upon the word came up in your mind first. example) If you were asked that 'Where is Tanaka?' In your answer, the place where Tanaka is' will be the first word you want to put. Then, you might say that '事務所に田中さんがいます'. In contrast, if you were asked that 'Who is in office?'. You might want to put Takana first in saying, '田中さんは事務所にいます'. However, this is not rule, just I talked about the inclination on the conversation. Thank you =)