In the game of go, errors are the most important. Games are lost due to your own errors and won due to errors of your opponent. Before any move, ask yourself if it is a mistake, or if a better, more effective move exists, which itself is no mistake. Evaluation of a move is done by consideration of its meanings, global context, and fitting tactical variations (i.e. opponent's responses). After a loss, analyze your game to find (the most important) errors. They may be of psychological nature. Remember your mistakes and avoid them in following games. Be patient in applying this learning process. A discussion with other players, especially with dans will be helpful.
The second important thing is life and death. A miscalculation of a group's status has a direct effect on a game's outcome. Before any move check the status of all groups and their strengths and weaknesses. Distinguish important groups and those that might be sacrificed. Closely related is the theme of cutting and connecting. This is to be seen in a global context as well as locally. Locally you have to find good shape: Shape that is resilient enough for connection and loose enough to be maximally efficient; shape that defends and also serves for attack. Your reading ability concerning life and death is a good indicator of your strength. You can improve by studying many Tsume-go problems. Choose problems that can be solved easily. You should read books, for whose problems you spend about half a minute to three minutes, rather than ten minutes to half an hour each. Do not choose problems that are too easy to learn from. Try to solve about 90% of all problems by reading, before understanding the given solutions.
Go is a game of harmony and war. Every state or action has its adverse state or action. E.g. an attack of the opponent's groups often weakens your own groups. If you take territory, you share it with the opponent's thickness.
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