Best not to learn a speech, but rehearse from bullet points and have those available to sooth nerves.
Eglantine19 - I did the mother of the bride speech and her stepfather just walked her down the aisle. Use the little silly handbag we have at these events, a set of cards with simple highlighted bullet points, but tied into order in case they are dropped, then go for it.
I ended up enjoying it, did the whole thing of explaining I had chosen that job in case I upstaged the bride or people had thought we were sisters if I had walked her down the aisle, said it was my opportunity to get my own back after 34 years. Knowing her well as her mum, I could relate bits from her being a 3 year old bridesmaid, through uni, and early career, with quips that related to some of the colleagues there. I could even steal the groom's stories of 4 hilarious attempts at proposal in paris, as he seemed bent on just saying thank you to everyone. Then I had witnessed the wedding preps and dress purchase in Bakewell, with compulsory puddings purchased by all of us, and how the retinue of attendants had grown and grown. So no "jokes" needed, just real humorous events. I had a photo book to present to her, and silly mugs. It was the shortest speech of the 3, probably but the best, even if I do say so myself.