With so many Instagram Apps on the market, it may be hard to choose which ones to use. Here are my favourites, bearing in mind I use Android and Google Chromebook exclusively.
This is a superb app that let's you know who you're following but is not following you back. Ideally you want to minimise the number of these people, apart from those you consider Influencers. On the flip side, I should reiterate that you should be interested in the people that you follow. They should have nice photos and/or are in the right demographic, otherwise it would be harder to find similar people to follow in the future.
As well as that, you can use the extra features (which cost a nominal amount, I think £0.77 per page). My favourite is the media insight page, as I can see which posts people like and engage with. I quickly learnt that more artistic shots work for me, instead of motivational quotes, pics of my tea cup (yawn), and random "life" shots (ie if they aren't my friends in real life, it probably won't be very interesting to my audience)
This app is great for reposting someone else's image, and allows you to copy and paste their text description automatically. This is handy as you don't have to remember the account you copied from, and will give them credit. It is also handy to use some of their hashtags, although I find it advantageous to add a few of my own. It is slightly different from some of the other ones I've seen, as it doesn't watermark the photo with the initial posters username (I think that looks quite messy)
This is my go to Social Media Managing Tool. I am able to schedule my posts in easily on Instagram. The only slight annoyance is that it doesn't post it for you, you still need to post it yourself (I don't think there is a Social Media Managing Tool that lest you post directly to Instagram, please let me know in comments if that's not the case). It does however have it ready for you to post. This means you can write the hashtags on a desktop prior to posting - I have found my autocorrect on my phone *really* annoying when I'm trying to get specific hashtags down (sort it out, SwiftKey), so I've found desktop working great. You can also download the HooteSuite app in the Google Play store (and presumably Apple iOS store); I actually prefer the look of the scheduler as you can see the images in the Publisher page (and you can't on the desktop version, which is a bit odd).
This is my go to photo editor. I operate off a Chromebook so I don't have access to Lightroom/iPhoto/Aperture etc but I've found it to be sufficient. I can batch upload/download photos, which many of the free editors don't have. I also have it on my desktop and Android phone, so I can use the same filter (I foam everything up to make my feed look consistent)
Boomerang is Instagram's own video app, it takes a burst of photos, then speeds them up and plays them forward and backward to create a dynamic short video. I love seeing other's boomerang vids (when done correctly), but I still haven't delved into it properly myself (partially because I think it messes up my gallery, and I'm a bit OCD about things like that...)
Instagram Apps I would not recommend
....anything that makes you post several pictures for one picture. They really annoy me, particularly if they are posted in quick succession, so they mess up my feed. Grr. If they are pictures in their own right, and posted after a decent time period, I guess I can live with that.
Also any of those things where you can buy followers. I haven't experimented with it, but what's the point of having lots of ghost followers? (accounts that don't interact with you at all?)