I'd like to share some of my strategies that has helped me so far :

1. Move very slowly. I hardly ever use the dash function, only meant to bring up my soldiers to the front line fast or shift angles for flanking purposes. I end 80% of my moves with overwatch. And when I do move, its with a leap frog movement.

2. Get your sniper to high ground and maintain overwatch. Grapples are great for this.

3. Stop and listen ! I sometimes just let 2-3 rounds go to just stop and listen. You will surpirised at the outcome.

4. Don't group up your squads ffs. Spread em out so that you can quickly react and cover your flanks.

5. Once you uncover a squad of aliens in the fog of war do no let other team members go to other parts of the fog. It's the same concept as pulling in mmorpg. Handle the enemy first then advance again slowly, unveiling the fog.

6. Once your lead soldier has uncovered the aliens, you have two options. Find better cover (if your flanking tactics for your squad is still intact) or retreat for better cover or vantage point (in the event u messed up as a commander and put your soldier in a bad position)

That's all I can think of for now. Some general ones :

7. Cash is king through out the game. Hence I feel starting in Africa is the best.

8. Scientist are useless at the start of the game but grow more important later

9. Build facilities that are the same kind side by side.

10. Sniper's are not meant to move alot. Get into position at high ground and stay there in overwatch. 

That's all I can think of for now.