My brother is a phenomenal board game player. As an older brother he was a cagey game player and driven to the point of almost ruthless [at least from my view as the younger sister]. To this day I have NEVER beaten him in a game of Monopoly®. Not terribly surprisingly... I am not an eager Monopoly® player. I remember my father telling me as an adult that he had sometimes played games with my brother so that my brother would learn how to lose and still be a good sport.
1- Pick short games. This way the chances of being willing to play again after losing are better. The chances of winning at least once go up because of the stats and playing more often.
2. Pick games that rely on luck. Any game that relies on strategy, accumulated knowledge, or planning ahead gives the advantage to an older, or wiser child. Luck based games add the frustration of bad luck vs good luck, but at least it is luck rather than skill or knowledge.
3. Teach the language of good sportsmanship. Before my kids could read I use only one or two phrases over and over each time I played with them, modeling acceptable language to respond to game emotions. Silly frustration words: [Slibbit!..... Balderdash! ....Dang!... make one up] When its not going well: Maybe next turn my luck will be better. When it is going very well: Boy, am I lucky right now. When they got old enough to read if they still struggled I made little index cards with comments they could choose from during the game.
That's the gist of it. If you need more ideas or specifics let me know. And for those of you who like knowledge based games I recommend you consider playing board review games with your kids periodically. The cool part isi that since you are using their school content for the basis, they may actually have an advantage over you... a powerful, exciting moment for any child! [See blog entry Feb 21, 2011: School Bell: Board Game Review]
Image credits: canberracyclingclub.org.au, writingasjoe.blogspot.com