There is one common thing that I have noticed in life that also applies to OverPower, practice makes perfect.  In other words, you will lose games, period.  But for every lost game there is also a victory.  One thing to consider is that you can learn more from a loss than from a victory.  What worked, what did not, and why.  When you win, it is easy to think you did everything possible right.  But in losing, many people will want to question what happened and move forward from there.  This is where your own personal understanding of the game can grow and improve.  No guide can make you a grand master champion just from reading it.  This web site can only show you where the light is at the end of the tunnel, but you must travel the distance to get there.  You must make the effort to try what does not often win the game to know why it does not work most of the time.  It is then and only then can you know that you have learned something, when you have applied it.
    Above all else though, OverPower is just a game.  I will not bore you with the names of other games I can assume you have heard of, but OverPower is just like most of them, it is just a game.  To this extent, OverPower is meant for you to have fun, and nothing else.  I believe that there are three types of people in OverPower.  People who play to have fun (the good), people who play only to win (the bad), and people who play thinking winning is the only way to have fun (the ugly).  This is just a general attitude people take into any game they may play, it is not meant to predict how anyone would respond to winning and losing.  Players who play to have fun are people you would want to play against.  These players will typically bring something to the game which makes it more fun to play, even for the eventual loser.  People who play to win are people you will feel obligated to beat, even if it is just to shut them up somewhat.  These people usually have something to take away from the game, like the other player's dignity, ability to have fun, and general care for the game.  Lastly, people who play thinking winning is the only way to have fun you will just want to plain never have anything to do with.  Usually, the bad and the ugly never know they belong to that group and I don't recommend telling them that they do, no matter how many other players believe it.  Do not play the game constantly thinking about what the "best" deck is.  Do not think about which characters are the most powerful.  Do try to break the mold that everyone uses the same characters.  Above all else, have fun with the game.