- Learn to use groups, create groups by dragging your mouse over units or getting units together by using shift key and naming them with ctrl + numbers 1,2.. Groups will help you with managing your army and gives you faster access to unit abilities.
- Learn to use healthpacks, Gabe must survive first mission but that doesnt mean he has to finish it with 100% of health. Picking up healthpack with your squad will reinforce it with new members increasing not only health but also your damage output, increasing your chance for success.
- Playing campaign on lower difficulty or playing multiplayer games will allow you to increase level of your elites and allows you to buy new elites, you can often bring new elites on missions which are more powerful than elites you are given in story. Also on level 3 elites unlock new passive doctrines which might help, for example you can use drop pods in first mission to heal your squads thanks to Gabes healing doctrine.
- Use unit abilities, they can save your life. Gabe can use his Q to escape or to easily reach ranged units, his W reflects projectiles and its aoe knocback can help you get melee units from your ranged squads, scouts have stun grenades proper throw can disable more than 1 squad in case you need to escape or stop them for some bigger nuke combo.
- Do not rush in. Its always better to see what will enemy units do, often AI units will work as a distraction. Sometimes progressing to a certain point will cause some things to happen, change of mission objectives, new enemy arrives etc.
First part of the game there is nothing to worry about. When defending breach your space marines will easily destroy all orks without your help, to make this faster you can run directly into breach and use W to deal aoe damage and knockback orks, also orks will have reinforcements dropping behind your squad, you can see indicators on the ground and prepare to defend, its preferable to defend heavy bolter team.
Small fight when you get your Q goes easily without your help, guardsmen will engage ork units and unreachable squad of scouts will help.
Small fight on bridge is quickly over when you push Gabe forward, to keep enemy units busy and stop them from reaching your ranged squads, and when you drop your marines directly on ork heads.
Second part is where game might get a bit more interesting. Your first bigger fight, do not rush in, use your ranged squads to attack and let the guardsmen tank the damage, only when they are all down or when some orks start charging your ranged squads, step in with Gabriel to stop them.
When you reach communication array you will first want to stay near the entrance, again dont rush, let the guardsmen do their job. Rushing in will cause more enemy units to come and you will find yourself in dangerous position, running too far in can cause easy loss of all units.
First part of this fight is to clear everything you can without leaving area around the entrance, second part is moving out a bit, this will cause more enemy units to arrive.
Prepare for third part by moving Gabe forward near the stair from where orks are coming for, soon ork heavy ranged squad appears and you can take them down with your hero, use your abilities to quickly travel the distance and keep enemy units from overwhelming you. Its better to run in with Gabriel, because your units can die before you are relieved by arrival of sniper scouts.