How to grow on Instagram?

Depending on what you do I've found the following has helped me:

HASHTAGS - Relevant hashtags in every post will help gain natural viewers and followers (along with some bots). I.E. You're a photographer, use #photography, #photographer, #landscapephotography / #portraitphotography / #etcphotography etc. etc.
LOCATION TAGGING - Tag location in every post, this can help bring local customers/followers/viewers.
COMMENT - I reply to every non-bot comment on my work, even if it's just using a few simple emojis.

Maybe this is basic, maybe it's something you haven't thought of but these things have helped me grow a great customer base along with consistent work.