A strategy at Uno may be offensive (aiming to go out), or defensive (aiming to minimize the value of one’s hand, in the event that another player goes out, thus getting those points). Part of the skill of playing Uno is knowing when to adopt an offensive or defensive strategy.
An offensive strategy would be holding on to Wild and Wild Draw Four cards because they can be played near the end of the hand in order to go out (when it’s harder to play a matching card). However, a defensive strategy would advise getting rid of such cards early, because they have a high point value.
A defensive strategy would advise playing a high card in order to reduce the point value of the hand. However, an offensive strategy would suggest playing a 0 when the player wants to continue on the current color, because it is less likely to be matched by another 0 of a different color (there is only one 0 of each color, but two of each 1–9).
A player holding only one card is required to call out “Uno” or risk being penalized if caught. A player who calls “Uno” risks being the target of concerted action by the other players, who may be able to use action cards to prevent that player from going out. Depending on the level and seriousness of play, some players may deliberately avoid saying “Uno”, in the hope of avoiding detection and then going out on the next turn. For this reason, it is useful to conceal how many cards are in your hand and to keep track of how many cards every other player holds.