one tactic I use is to just mimic or imitate their every move...some people find it distracting/annoying, hence creating openings.

Another one i like is the fake low kick before switching it to a roundhouse kick to the head. pretty effective in the first round.

One of my favorite tactics is throwing a sidekick, and if they block it, using the leg to literally push them back. You need to be very quick, or they may scoop your leg, but if you're fast enough, you'll throw them completely off balance. The key then is to pop in, but don't go for the attack. In my experience, in their desperation to regain balance, they'll rush forward with an attack. So you pop in and angle off quickly. Throw your attack then.

back fist
reverse punch
round house
side kick.... not in exact order.
Bottom line... basics. Master the basics and everything else follows