You can preview the line of sights (enemies in sight) in the options (this changed my life, no more positioning only to discover I can only overwatch).
Hit percentage odds are also in your favor, the percentages shown are way lower than the ones the game actually use.
While some bugs are game breaking (impossibility to get some unconscious soldiers, sudden team discovery because of broken coding of the lost, etc.), some are totally in your favor.
For example, you can manipulate the enemies to group on a random point of the map. I remember having a group of at least a dozen of end-games enemies in the last mission politely acting as sitting ducks. The poor souls were grouped while I had claymores + saturation fire + zone psi attacks.