There are a few key areas to a speech that will dictate its success, and whilst structure and great writing are obviously important, nothing really determines the outcome of a speech more succinctly than its length. If everyone kept an eye on the length of their speeches, then we wouldn't be subjected to the the 90 minute speech marathons that collectively wedding speeches can become. It's always going to be a fine balancing act - on the one hand you don't want to talk forever and bore everyone senseless, but on the other hand you don't want it to be a couple of sentences and then a toast. However, if I had to choose how to ruin my speech, it would easily be the latter option.
You could have the most amazingly well written speech, a great structure and genuinely funny lines, but if you talk for too long, it will all count for nothing. In my mind it's virtually impossible to talk for 7 minutes and not start repeating yourself in some way, which is of course what an awful lot of speakers do. Not content with saying how amazing their daughter is in just one way, they do it in triplicate, which is as pointless as it is really boring. The temptation to speak for longer than necessary usually comes from the desire to cram far too much into a speech, and you have to remind yourself that this is for the audience not you. They will never know what you didn't put into the speech, so just make what you have got in there really good.
This is particularly tricky when it comes to making the father of the bride speech - you're trying to cram 30 years of someone's life into a 7 - 8 minute speech. So, you have to be ruthless: if it doesn't add anything to the speech, if it's similar to something you've already mentioned, or if it just isn't funny enough, then cut it. The best speeches are easily the most efficient ones, and as the father of the bride is the first one up, he needs to lead by example. The last thing any wedding needs is for the father of the bride to talk for 30 minutes and pretty much render the rest of the speeches as some kind of endurance test. I recently heard of a father talking for over an hour, using a Powerpoint. Someone should have taken him out with a bread roll.
Keep it to a talking time of around 8 minutes, and the word count to about 1350. Talk slowly, enjoy yourself, and make others enjoy it even more.