Basic Skills
You need to master two basic skills:
1) Find out the only possible positions of the mines from a certain number:
For the following case:

Only one covered tile is adjacent to the circled tile, and therefore that covered tile must contain a mine:

2) When all mines from a certain number are found, clear all remaining tiles:
For the following case:

You have already found the mine for the circled tile, and therefore all remaining tiles must be safe:

1) Find out the only possible positions of the mines from a certain number:
For the following case:

Only one covered tile is adjacent to the circled tile, and therefore that covered tile must contain a mine:

2) When all mines from a certain number are found, clear all remaining tiles:
For the following case:

You have already found the mine for the circled tile, and therefore all remaining tiles must be safe:

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