Pictures that a longer vertically than horizontally utilize more screen real estate, and therefore spend longer on the screen when scrolling through a feed. Users have suggested in the past that they notice more likes on pictures that are orientated this way.
A comment pod is made up of about 10-15 people. This group always likes and comments on each others pictures. This becomes most beneficial if it is done as soon as a picture is posted as it helps boost the instant visibility of the post. The more followers each member has, the more benefit it is to the person who posted the picture.
Usually these pods exist via the DM feature on Instagram. When someone posts a new picture, they also share it to this group so that the group is notified and can instantly go and like the image.
These pods work best when everyone in the group has the same niche, as it means everyone's followers are more likely to also like the content.
A much hated tactic by many, but without a doubt one that works. I discourage the use of this, but it is such a popular technique it needs to be stated - at the very least, so you can understand when it happens to you.
The idea behind this is that you will follow a user and they may follow you back. After 2-4 days you unfollow them and hope they don't notice, leaving them following you.
In reality, why bother unfollowing them? Just follow them and like their images whenever you can. You'll come across much more genuine and you'll also avoid the risk of losing them as a follower.
This is considered a scummy technique to use by many, and with the amount of people that use apps to keep track of followers, it is less likely to work.