You need to decide on the mood or the tone of your speech. It can be humorous, serious, emotional or romantic. You have to keep in mind that close and distant relatives both are present on the wedding and also there are multiple age groups, so your speech should be appropriate. Also consider the length of the speech as you are not the only one talking at the event. You do not want people to get bored with too many speeches which take too long.
No bride’s speech is complete without the mention of the groom in it. What you want to say depends on the type of relationship you both share. People are very much interested in listening to how you both met, fell in love, who proposed and where etc. Add some of these details to make it interesting. It is up to you how much information you want to share or keep private. It is generally advisable to use humor in the speech. Jokes keep the mood light and everybody enjoys a good laugh. Just make sure you do not get too personal.
The speech is also the best chance to thank all the people you want. The list includes your bridesmaids, parents, in-laws and the guests for being there. Do not start taking a lot of names and make it into a long list because nobody will be very interested. Also thank people who have come from far off places or older people who still made it even though they have health issues.
Lastly do not get so drunk that you lose track of what you are saying. It is justified that you are very happy and can indulge but leave that for the after party.