There are many pitfalls in wedding speeches, and they're all different depending on what speech you're making. Many best men like to talk about themselves far too much, and grooms like to go into granular detail about every single usher and how wonderful the florists have been. However, when it comes to the father of the bride speech, the classic mistake is actually not talking very much about you daughter, sometimes not talking about her at all. Fathers of the bride can get so carried away with 'ice breakers' and welcoming poeple, and recounting the last time they had to make a speech, that before they know it, it's the end of the speech, and all they've said is that their daughter looks lovely. I actually once worked for a mother of the bride who didn't want to say her daughter looked lovely, as it wasn't true. Unbelievable.
Yes, it's your job to kick things off and thank and welcome people, but the only reason you're up there is to talk about your daughter. It's your one opportunity in life to say exactly what she means to you, and if you're not going to bother, then leave it up to the groom. Sometimes there are tricky relationships between father and daughter, usually where a divorce is involved, but by omitting to say anything, then all you're doing is throwing a spotlight on to it. Make sure that at least 50%, preferably more, is about her, and the rest should be evenly spread between your new son in law, family and friends. On the other hand, you can go too far. I recently wrote a 1500 word speech for a client, who thought as I'd written 198 words on the groom, this was going too far and there wasn't enough about his daughter. You need a sense of balance, and this clearly wasn't it.
Another classic gaff is to make this speech just from you. Sometimes, through bereavement and challenging family circumstances, that will be necessary, but for all other occasions make it on behalf of you and your wife, and don't froget to say what a great job she has done in shaping the fine young woman your daughter has become. In fact, you also need to do this when there is divorce involved, because if your former wife is sitting there and doesn't get any recogition, then that type of omission lives long in the memory.