1. If you're not the funny guy, don't try to be.
A Wedding is an immensely important event for couples, and they have chosen you to bless them with a toast on the big day. If your forte is not comedy, the wedding day is not the time to try your hand at being a comedian.
2. Keep it short and sweet.
Remember, it's a toast, not a speech. No one wants to sit through a 10-minute toast, no matter how good. There is dancing, eating, and drinking to be had and you are not the main event. A concise toast that packs a punch is more powerful and memorable than a drawn-out one.
3. Stay positive.
The toast should be celebratory towards the honorary couple. Do not bring up their ex's or negativity from the past. Today is a day for love and happiness, so your toast should reflect that.
4. It's about both of them.
Sometimes it's hard to give a toast that speaks to both the bride and groom when you know one better than the other (ex. sisters, brothers, cousins, roommates, etc.) but the Wedding is a celebration of both. Try to keep the recollections to a minimum and focus on the beautiful future ahead.
5. End with a bang.
A powerful quote or a clever tie-in to the rest of the toast is the perfect way to end. It let's the guests know you have finished speaking and leads nicely into raising your glasses and toasting to the beautiful couple. Sentiment always works.