If it was my speech, I would say that you think that the groom and the bride are good together, and that they make a wonderful couple, say that the bride looks lovely and say how lucky they both are to find happiness and true love, as it is rare to find these days. Then crack a few jokes about what you and the groom got up to in the past (not the stag night though) and say how nice the bridesmaids look, and the mother of the bride.