If you want to get more followers, you need to set your account to public so people can easily view the content of your instagram. But the more important thing is to make your account appealing to people by posting interesting stuff. In my opinion, you cannot really get more followers unless you offer them something they can make use of. I would advise you to focus on what you like most such as general photography, architecture, pets, arts, music, books, etc. Taking decent pictures also plays a huge part. You may try using programs such as Adobe Lightroom or Adobe Photoshop to improve the quality of your photos.
In case you just recently created your account, it will be helpful if you first follow all your Facebook friends who already have an Instagram account. Once they follow you, you will then appear as one of the Suggested Persons to other people who are new to this platform.
The next thing you need to do is to stay active. People will easily notice you if you regularly post something. And by posting, I do not mean plain photos. You also need to be creative with the captions. Captions and optional hashtags make a post more appealing to people.