A lot of writing speeches and toasts is from listening to other ones. Talk to the person-who-you-are-toasting's friends and family to see if there are any stories that would make a good toast. You'd be surprised at some of the things that you can find out. Of course, the really embarrassing ones should be saved for bachelor or bachelorette parties.
You may also want to find a poem that relates to them and read that aloud. Poems are always good emotional material. Try to find ones that speak of married love, rather than the newness of love. This will demonstrate your faith in their new marriage, rather than concentrating on the courtship.
Be sure that your glass and the glasses of your guests are filled. You will want to raise your glass with your right hand, approximately shoulder height. Now make your toast, and drink up! If you have difficulty writing a toast of your own, we have collected some below to give you some ideas.