This page assumes you know the rules of Klondike. Each point below is something you can check on the table in front of you. Try them on the game on the home page, or on the daily deal so you can compare with friends.
Aces and 2s should go up at once. They are never needed in the tableau. For higher cards, use this check: a card is safe to send up when both cards of the opposite color and one rank lower are already on the foundations. A red 6 is safe once both black 5s are up, because nothing else would ever be placed on it. If one of those black 5s is still in play, the red 6 may be the only place it can go, so leave the 6 in the tableau until you need the space.
An empty column helps only when a King can fill it, so do not clear one with no King available. When you have a choice of Kings, pick by color. If the queen you need to free next is red, put a black King in the column, so the queen has a home. Prefer a King that has face-down cards under it, because moving it turns one of them over. A King from the waste turns nothing over, so it is usually the weaker choice.
With unlimited passes, a pass through the stock costs nothing, so it is worth one early look to learn where the Kings and low cards are. In Turn 3 the order of the waste matters: playing one card shifts which cards come up later. The Turn 3 page explains how to plan around this, and the Turn 1 page covers the easier mode.
Some deals cannot be won. If every face-down card in a column is stuck under a King-headed run that has nowhere to go, and the stock offers nothing, that column is closed. The game tells you when no useful move is left. At that point a new deal is the right call. The Klondike page has more on how often deals can be won.
New to the game? Start with how to play Solitaire. For a game with no hidden cards, try FreeCell. For a longer one, try Spider.