I say this as a woman - usually the maid-of-honor speeches are TURRIBLE and sappy (someone's usually crying), and so the best man speech honestly doesn't have a lot to which it needs to aspire. You'll do great, but just know that if you can keep from sobbing, you're probably already in the lead.
I've done a large amount of public speaking over the years. Janny and I did a joint wedding toast at a huge wedding once for which we had not planned on doing anything until five minutes before the speech when we were asked, yet we had people asking us how long it had taken us to write it (that's totally not to brag, it's just to say that you CAN do it extemporaneous and be fine). If you're comfortable with public speaking, you can be more off-the-cuff. Have a general overview in your head of a couple of good stories, and work those into a theme. If you're not a public speaker, maybe have it broken down a little more formally in your mind, or even have a notecard that you leave ON THE TABLE (rather than in front of your face) with some main bullet points.
The best wedding toasts, IMO, involve a funny story about the person you specifically are honoring, or the couple together, and how that story is representative of why the marriage will work. My example above w/Janny and I involved that, which is why it worked. At our wedding, one of J's brothers got up and told a story about one of the brothers stealing something of Janny's, and him riding a bike for a long, long time just go get it back and beat up his brother (or similar). He summed that up by saying Janny was willing to go any distance once he has committed to something, etc. It was adorable and funny, and it had something for people of all ages and genders.
I've done a large amount of public speaking over the years. Janny and I did a joint wedding toast at a huge wedding once for which we had not planned on doing anything until five minutes before the speech when we were asked, yet we had people asking us how long it had taken us to write it (that's totally not to brag, it's just to say that you CAN do it extemporaneous and be fine). If you're comfortable with public speaking, you can be more off-the-cuff. Have a general overview in your head of a couple of good stories, and work those into a theme. If you're not a public speaker, maybe have it broken down a little more formally in your mind, or even have a notecard that you leave ON THE TABLE (rather than in front of your face) with some main bullet points.
The best wedding toasts, IMO, involve a funny story about the person you specifically are honoring, or the couple together, and how that story is representative of why the marriage will work. My example above w/Janny and I involved that, which is why it worked. At our wedding, one of J's brothers got up and told a story about one of the brothers stealing something of Janny's, and him riding a bike for a long, long time just go get it back and beat up his brother (or similar). He summed that up by saying Janny was willing to go any distance once he has committed to something, etc. It was adorable and funny, and it had something for people of all ages and genders.