Werewolf is a social deduction game. A small team of werewolves exist in a village of humans, but the identity of who is a human and who is a wolf is unknown to the humans. Each "night" the wolves get to kill one village player; each "day", the village (after thorough discussion) lynch a player who is believed to be a wolf. The villagers win if they lynch all the werewolves. The wolves win if they kill all the villagers. It may appear to be a silly social game where players get to call each other liars and have fun being a good "actor" or "actress". But, there is actually deep strategy involved. Below are a few general strategies that can help players improve their odds of winning.
Lies are crucial, especially for a werewolf. You have to blend in with the village, even going so far as to claim a role and explain why the real holder of that role is a lying wolf. Lying may benefit you too if you are on the village team. Villagers do want to have everyone claim what they are right off the bat, as they believe that wolves will be among those claiming to have the same role. But one has to remember that the wolves already know who they are. So having everyone claim is just letting the wolves know who the tastiest villagers are, and the village team is expected to lose their seer/hunter/guard/witch quickly. Instead, there are reasons why players on the village team may want to lie. Claiming to be something you are not may distract the wolves and add uncertainty and doubt to their minds. Doing so also gives cover for the people who actually have those roles, allowing them to fly under the radar a bit so that they can use their special powers a few more times.
Quiet people could be dangerous, as being unnoticed is great for a werewolf. Villagers who choose not to express their opinions except their vote do not provide any useful information and hence aren't helping the villagers survive. A quiet player is either useless or a werewolf, so eliminate them is a good decision either way. This is especially true in the early rounds, when the information revealed is very limited.
Even though it is important for the villagers to create consensus, that consensus can sometimes be manipulated and work to their disadvantage. As a villager, you need to keep an independent mind.
Experienced players know what they are doing. An experienced werewolf is more dangerous, and an experienced villager is more useful. Novices tend to act randomly so that finding out who they are does not help you too much. Experienced players on the other hand come up with good reasons for suspecting people, and checking out their identities early will let you know if the "reasons" are bluffs or not.
If you check out a villager and know s/he is a villager, you can tell the person what you know. Of course, at the same time, a werewolf can act like the seer and pretend to do the same thing. So if you are a villager and this happens to you, keep in mind that all a whisper like this really means is that the other person isn't a villager.
Make sure people see you accusing, and more importantly, weighing the evidence. The villagers know that if you don't have to think it over, you're a werewolf. Let them see you thinking it over.
People keep a close eye out for factions. A group of people who automatically trust one another are deemed suspicious, because only the werewolves have enough knowledge to trust each other. So, you are a werewolf, you want to act like you don't lay your trust on any of your fellow werewolves. If people notice you acting as a group, you will all be hanging from the trees.
The seer is a valuable asset, and no villager wants to loss the seer. By saying you are the seer, you make people feel more cautious about killing you, and meanwhile twist their thinking. Either you lead them down a wild goose chase, killing innocent people, or you force the real seer to reveal his/her identity. Either way it's a werewolf win.
The key is, nobody knows if the person who claims to be the seer really is the seer. Therefore if nobody kills the alleged seer, that person probably wasn't the seer, but rather a werewolf. That makes all information provided questionable. If somebody comes forward as the seer, and his/her credibility is in doubt, letting the person live can intensify the confusion and create the dissent you need. However, not killing the seer is an infinitely complicated strategy compared to the simpler version: killing the seer. If you are a werewolf, and you think you know who the seer is, and they haven't come forward yet, then killing the seer is a no-brainer. Likewise, if the seer comes forward and people trust him/her, kill the seer. You would only let the seer live if his/her credibility was in doubt.