just 3 steps :

1. click here to setup your share2steem account with steemconnect
2. link and verified your instagram account : Under 'social network' tab, click 'link account' button and select instagram and follow the instructions there.
3. On your next instagram post, use #share2steem anyway in the post but make sure it's the first 5 tags you use in the post. A few seconds later, you should see the post auto post to your steemit account.