Always be a good guest and have a lot of great reviews. Always leave great reviews if hosts deserve them.
Before traveling to a new place, find a bunch of airbnb apartments and put together a standard message template: who you are, why you need the place, a couple of questions about things not specified in the description (e.g. street address/location, wifi, etc). Send that message to all the hosts of the apartments you are considering. If you have a good reputation on AirBnB and want to stay longer term, you can also politely ask for a small discount.
Also pay attention to booking flexibility (fixed/moderate/flexible). I prefer flexible because I can always cancel even in the middle of my stay and just pay for one more night.
I also target places with at least a few good reviews and a 5 star rating or close. Another strategy is to target new hosts who probably offer lower prices and/or are more willing to negotiate. I skip places with at least one bad review unless it's clear the reviewer is a weirdo. Also, AirBnB leaves automatic reviews if a host cancels a booking before the trip and how many days in advance they cancelled. This to me is like a black mark: i never contact those hosts. The only exception is if it happened a long time ago and there are many recent great reviews and high average rating to make up for that.