Guile returns and still hasn't learnt any new special moves since he appeared in Street Fighter II.
That means you Guile veterans will know the drill by know - spam Sonic Booms to control the screen and force your opponent into making a mistake.
You have to learn various anti-airs to make your Guile effective, as Flash Kicks don't always cut it. Jump back HK, air throw, back + MP and cr.HP all work in different situations.
Sonic Boom (back, towards + P)
This is what you'll be relying on most of the time. You want to control the pace of the match by flooding the screen with Sonic Booms, before punishing their reckless ways to try and avoid it. EX Sonic Boom is incredibly fast and also beats Focus Attacks, so it's worth saving meter for.
Flash Kick (down, up + K)
Apart from EX Flash Kick, the standard version is hit and miss as an anti-air move. Sometimes it will hit opponents clean, sometimes it will trade, sometimes it will miss altogether! Its best use is to finish combos, otherwise stick to the EX version.
Double Flash (down/back, down/towards, down/back, up/towards + K)
Guile's Super is decent as an anti-air, combo ender and to punish blocked moves with because it starts up so quickly.
Flash Explosion (down/back, down/towards, down/back, up/towards + KKK)
This Ultra is fairly inconsistent too, as it sometimes misses the last kick if you tried it as an anti-air, not to mention it doesn't always work as an anti-air because the start-up is a little slow. It's best used after a Focus Attack crumple or when predicting your opponent will stick out a limb.
Basic Combo: cr.MK > towards + MP
Advanced Combo: Jump in LK > cr.LP > cr.MP xx Flash Kick