Your top priority should always be to reveal hidden cards in the tableau. More face-up cards = more options.
Try to keep all columns at similar heights. Avoid making one column very tall while others remain short — this limits your flexibility.
Empty tableau columns are invaluable. Only Kings can start an empty column, so save your Kings for this purpose.
Don't rush to move cards to the foundation. Sometimes keeping a card in the tableau gives you more options for building sequences.
Go through the stock pile systematically. Remember that after the first pass, you know the order of all cards.
Before making a move, check if it will block other potential moves. Sometimes the obvious move isn't the best one.
Try to keep a mix of red and black cards accessible. Getting stuck with all one color is a common losing pattern.