Try using a timer to time the length of your speech. This ensures your speech fills the time you have. If you find that your speech is very short, consider beefing it up with a little research. It is important not to rush through your speech.
If you are preparing for a public speaking engagement in advance, memorize your speech first, before anything else. Once you can recite your speech from memory at any point of day, then you can work on delivery. Knowing your speech by heart will also enable you to ad lib if necessary, once you're at the podium.
It's vital to know about everything that you will be talking about during a speech. It is useful to know all the facts, figures and a few jokes or stories relating to your topic, whether your speech is memorized or not. Work them in where you think they fit and will engage your current audience. Have a question session at the end of your speech.
After you memorize your speech, you should practice it over and over. This is the time where you can perfect the speech with effective changes. Also, practice your breathing and pace. You will need to leave pauses for interruptions by the audience. If you can, practice your speech with the exact equipment you will have available at the time of your speech.
You can be good at speaking in public. You just have to practice. All these suggestions will definitely help with that. Practice them in all of your social interactions. With time, you will begin to feel comfortable with public speaking. You will appreciate the benefits.