It won’t be easy to make one single step. It will be better for you to check your guns often and get the latest upgrades for your weapons.
There are many upgrades that you will need on your mission. Be sure that you can make your best score on each stage. Power ups, multiple kills, wombo-combos and headshots add points to your score, so try to make the best gameplay!
Besides, you have to protect yourself with the environment, trying to defeat enemies before they hit you. Move around the playing area and its different covers to get a good angle to flank your foes.
You always have multiple ways to complete a zone. Try all the possibilities and select the one that fits better for you.