Medium games are Barbu and Last Two. Easy games are Trumps and Fantan. The absolute most basic strategy of Barbu is to strive to call hard games as early as possible and to save easy games for the hands which are forced calls. The optimal game to leave for your last call is Fantan, because near the end of the game, players look for any excuse to double dealers who might have been forced to call a game that is grossly unsuitable for the hand dealt. While unsuitable hands for Fantan are not altogether uncommon, hands that can double are much less so, because the rank of the base card is not known until after the bidding.
Trumps is also good to keep until the end because hands that can double trumps calls are rare.
Trumps is almost never doubled except in the last round, so it is optimal to call it in the second to last round. In general, good strategy is to try to avoid being doubled. It is very easy to lose huge numbers of points when doubled, even if holding a good hand. Aiming is helpful. It is worthwhile to gang up on the leader because it is much easier to take points away from someone than to gain them.