I have never built an engine for such variants, and hardly ever played them myself. But strategy is much more subtle than you might think. From other engines (like Sjeng) I know that piece values are different from Chess, but positive. E.g. a Queen is worth about 6 Pawns. To win you must get a controlling advantage, so that you can force the opponent to take your weak pieces, which otherwise are difficult to get rid of. E.g. when white has all pieces in the FIDE start position, and black only his King and Pawns, white very easily wins.
I have never built an engine for such variants, and hardly ever played them myself. But strategy is much more subtle than you might think. From other engines (like Sjeng) I know that piece values are different from Chess, but positive. E.g. a Queen is worth about 6 Pawns. To win you must get a controlling advantage, so that you can force the opponent to take your weak pieces, which otherwise are difficult to get rid of. E.g. when white has all pieces in the FIDE start position, and black only his King and Pawns, white very easily wins.