You are not British (unless you are, in which case I'm sorry to hear it). Make your details specific and your feelings transparent, but keep the tone upbeat. No embarrassing stories about ex-girlfriends/boyfriends, the one who got away, etc. No embarrassing stories about things the bride or groom did while under the influence of booze/weed/Bernie Sanders. NO EMBARRASSING STORIES.
2. Have a theme and a landing point firmly in mind.
It's not about you: All the guests need to know is your name and, in the briefest possible way, how you know the bride and/or groom. It's about them: what makes Sue and Joe different from every other couple?
Your central conceit should be easily graspable by two hundred people of varying intellect and sobriety. Joe was always looking for X in his life, as exemplified by stories Y and Z. (The stories you alone can provide. If you don't have singular insight, why stand up?) Then Joe found Sue, whose startup made an app that crowd-sourced X.
Or: Sue once told me the most important thing in a man was X. Then, when she met Joe, she worried that he had too much X. Until she realized that she'd never understood before what X really meant—and that was the night she proposed to him...
Or: Sue was always looking for X. Then she found Joe—who absolutely hated X. But Sue and Joe found happiness together in their mutual love of Y. And the funny thing is, from where I stand today, Y looks an awful lot like X...
3. Practice over and over, till you know the toast by heart.
Time yourself: Keep it to five minutes. Seven, tops, if you're the maid of honor or best man. Nine only if no one else is giving a toast and you have a fatal disease.
Practice once more out back or in the bathroom, just before go time. Then you'll be able to relax, read the mood in the room, slow down, and enjoy yourself. But keep a Post-It with the key beats in your pocket, in case. Nothing worse than grinding to a halt with "Anyway... I just love you guys so much!"
4. Have you learned something from Joe and Sue's relationship?
Some powerful truth about the nature of human fealty? This is your best, and maybe your only, chance to voice that truth. Weddings and funerals are when you need to bring your A game. Your candor will feel so beguiling that everyone at the wedding will fall in love with you, and the happy couple will forget all about how crappy your gift is.
Second-best cook in my household; no chance at being the best. Big believer in making dishes in large quantities, so our twins can eat them for several months afterward. Two party tricks: cracking two eggs at once, and carving a watermelon into the shape of a whale (a sprig of parsley makes the spout).