I have a growing amount of instagram followers, in my observation, posting too much in a day lessens your followers, also posting pictures that always have your face also lessens your followers, because most people judge you and most of them hate those people who post too much of their face. Posting a good quality of photos also help, connecting it with your facebook account and following your facebook friends on ig also helps, also putting your ig username on or fb bio under websites is a good promotion to your ig account. Use hashtags but dont overdo it. Follow people that you know are active as well. Don't be too vain