Just as in chess, a fight match may have any number of possible openers (these are specific to competitions), but may also be found in self-defense scenarios. Each opener has a different sort of strategy involved.
This is otherwise known as "feeling out the opponent." It takes a less aggressive approach, as in this phase, especially in the first round of match-up, fighters for the most part do not know what to expect, how their opponent will react to different stimuli, etc. A fighter who is feeling out the other will often throw test strikes and fakes to gauge the reaction of the opponent. A less experienced fighter may do this out of insecurity or fear; they do not want to make a costly mistake. A more experienced fighter may use this type of opening to "download" the opponent's timing, rhythms, reactions, etc. They also may be a more reactive type of fighter, looking to counter or waiting for the opponent to make a mistake. A good response to this is to simply force the action and not allow the opponent the room to breathe that they want. A blitz opening is also a good counter to this type of fighter, as it will likely catch them off-guard.
This is when a fighter comes out and begins pushing the action, and the pace may vary from slow and steady to pushing the action. This is typically done by a more confident fighter. They don't want to waste time dilly-dallying. This also forces the opponent to play at your pace or retreat. A more experienced fighter will still be able to size up the opponent's reactions and techniques from a more intense pace. One strategy to combat this is to change the pace and keep them from controlling the fight.
Sometimes and opponent comes out swinging for the fences. They want to overwhelm the opponent with a flurry of strikes and takedown attempts. This may create an early advantage, especially against a less experienced opponent. Some fighters are simply hoping for a quick win, and this may also be a tactic of a less confident fighter. The drawback to this opening is if the blitz doesn't have the desired effect, a lot of energy is expended. A more experienced or confident fighter can withstand a blitz and tire out the opponent or force them into a different pace. If an opponent opens with a blitz of strikes and no takedown attempts, this may signal that they prefer striking, and might be less comfortable on the ground. Opposite of this, a fighter that is better on the ground may attempt early takedowns, therefore one should attempt to force the standup game.