UPDATE: Steppes has now been re-added to the map cycle as well as some other maps as of August 2015. I never found Steppes while going for this acheivement and that explains why!
The most important thing about this achievement is knowing how to even find the maps!!
These Tier's should apply to finding Steppes as well: After many games I found that Tier's 5 and 6 gave me the best chance of finding Highway, although I once got Highway with a Tier 4 Artillery. I didn't try out Tier 7 and above simply because of the silver, time, and not having very many of them..However, it's really frustrating trying to get these maps as it is so random.
I alternated between 4-5 different Tier 5 and 6 tanks while trying to get the right maps.
Highway is a rather open map. Steppes apparently is even more open with slight hills and looks like fun!
My loadout was the US Tier 6 M4A3E2 using the 105MM gun. I find that gun extremely effective against almost any other tank especially if the enemy is not a heavy or it's side is quite visible.
I basically hung out in the center of my team, not quite at the front until we were definitely winning, when I rushed across the map looking for kills. It felt quite easy, but I think the tank you choose is very important to use well.
With my Medium M4A3E2, I have very good armor for the Tier. If I was choosing a light tank, I would've been trying to maximize my scouting ability for the XP instead.
Here's the video of my match; I had a few fortunate kills, and generally it was a very good round!