Scanning – basic process of iterating through the grid to detect best placing opportunities
Cross hatching – analyzing row, column and section to eliminate impossible numbers and limit possible ones
Box line reduction strategy – whenever you have a candidate which must belong to a row it can be ruled out as candidate in matching column and section (row,column section can be placed in any order)
Nishio – guessing strategy of elimination, place one candidate and eliminate all placements which are made impossible
Ariadne's thread - in this strategy board state is recorded,then replicated to a test copy, then a cell is selected which can have only 2 candidates, when substituted, as many pairs as possible in other cells can be determined. One of the numbers in the pair is selected and substituted into this draft. There is a 50% probability, the decision will lead to a dead end - which means that the selected number was incorrect. In this case, you need to "rewind the thread" - go back to the "original stae" and select and substitute a different number. If there were no errors in the decision, the substituted number will be the only true one.
But you still need to practice. Try your skills.