I get asked this question ALL the time. The truth is, there isn't necessarily a right answer. I think I would be doing each of you a disservice if I didn't tell you, everyday is ideal. Being in front of your followers and showing off your products, blog posts or services as often as possible is never a bad thing.
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That said, I don't think there's ever been a week where I've posted every single day, and guess what? I've continued to grow my Instagram (using the same strategies I teach in Post and Profit). I used to get SO stressed when I would read articles that said the only way to grow was by posting daily, even though I was consistently growing my account with just 3-5 posts a week. The proof that I didn't need to post every day was literally, right in front me, and yet I was determined to believe otherwise, because "that's what I heard."
My advice is to post "frequently." You can determine what frequently means to you - if you can get a quality photo up everyday, awesome...do that! If, like me, you're more of a 3-5 photos per week kind of person, awesome...do that! Develop a schedule that works for you, one that allows you to post QUALITY photos consistently (whatever consistently is to you).
Missed last week's Instagram Tips blog post? It was all about creating pretty Highlight Icons. Catch up here.