This trick use the combination of

1. Weak pkmn in first position in party
2. Give the pokemon Exp. Share

If u just use one of the trick, the pkmn will get 1/2
of the exp, and other 1/2 to the tanker.
BUT!, if u use both tricks, you're pkmn will earn 1/2
exp (as it should) + 1/2 from 1/2 exp of the tanker!

Example : Single battle against lvl 50 Fearow will give 
1157 exp (i think..). if u give Exp. Share + put the pkmn 
in front, it will get 579 + 289 = 868 Exp!

I'm sure it will help ya!