These are known patterns that can be used for all the enemy types in the game. Every one of them has been confirmed by me personally, and I have allowed no guesswork to go into them. I make no claims that every single possible pattern is here, so don't stake your life on that
A, G, and B; short for Attack, Guard, and Break; all refer to what the enemy is doing, so what you should be doing is the option that beats it. So G when it says A, B when it says G, and A when it says B. This is the most important thing to keep track of.
W means the enemy is doing nothing, so you can do whatever you want (except for Guard, that's just pointless).
[S] means the enemy is using a Skill, so plan accordingly. I do not have what the Skills do listed. That is beyond the scope of this page. For the Boss Servants specifically, you can find information to help with that in the boss strategies on the main walkthrough.
[EX] means the enemy is using his/her Noble Phantasm, so make sure you are prepared.
X means I'm not sure, so use your best judgment.