Summarize this article:

Most bottles will be covered by a label and you may want to remove that label so that your message in a bottle is not mistaken for trash.  To remove the label, place the bottle in hot water and let it sit for at least one hour. The hot water will loosen the glue on the label and make it easy for you to peel the label off. You may need to scrape some of the glue off of the bottle. Fill the inside of the bottle with warm soapy water and cover the opening of the bottle with your hand. Gently shake the bottle up and down for at least 30 seconds to remove any substances from the inside of the bottle. Pour out the soapy water and rinse the inside of the bottle with warm water. Once you have removed the label and cleaned the inside, place the bottle upside down in a strainer and allow it to dry. It will take about one hour for the inside of the bottle to completely dry, depending on the temperature in the room. You can also allow the inside of the bottle to dry overnight.  To dry the inside of the bottle more quickly, place it in the oven on low heat at 150 °F (65.6 °C) for approximately 25 to 30 minutes. Be cautious when removing the bottle from the oven and allow it to cool off before continuing with the process.   Another alternative for drying the inside of the bottle is rolling up a paper towel lengthwise and placing it inside of the bottle. Be sure to leave a portion of the paper towel on the outside of the bottle so that it can be easily removed.

Summary:
Remove the label (optional). Clean the bottle. Dry the bottle.