Raiding is made up of you spending 1,000 gold to search for an opponent and obtaining Glory points from them. it is very costly to find superb candidates to attack and take a good amount of glory points. Be careful not to attacking some who is to powerful. In some cases it is best to move on from high glory point yields as they are highly protected and there is a reason they have so much. You only have 5 attempts at which you may raid from but it can be refreshed with purchases with gems.
When you log off, your Player will be defended by the last Deck Selected. If you have been using specialized Decks for defeating certain Dungeons or Guild Maps, it is important to remember to switch Decks to your standard or defensive deck to ward off enemy's attempts at raiding your Glory Points and Creature Shards.
It is also important to note that the amount of Glory Points lost during raids is correlated to the number of Glory Points you currently have pooled. By remembering to spend your Glory points when you can before logging off, you will minimize the amount of Glory Points lost to raiding.
Shields are not too important but can keep you from loosing tons of glory points from people. in any circumstance you should wait till your shield is completely ran out before you attack. but you must especially make sure when you stock up for when you get a new hero or when you are going to refresh talents on your hero. You may spend 60 gems to obtain a 10 hour shield if need be.
Through battle log you can see how you lost defensive Raids in your absence and is a good way to determine upgrades and optimizations for your deck and identify your decks weaknesses.
Regardless of the outcome of Raids, the system allows you to counter-attack people that have previously attacked you through the Revenge System. This can be a great way to reclaim lost Glory Points or acquire even more Glory Points once per day for free, with multiple Revenges possible if you're willing to spend Gems.