Any glass bottle will do for your glass art. This includes, but isn't limited to, soda bottles, beer bottles, wine bottles, condiment bottles, perfume bottles, and so on. Before your chosen bottle is ready to melt, you need to make sure it is clean and dry. This includes any labels or even fingerprints that may be on it!  Labels that are difficult to remove can be soaked in hot, soapy water. A good soak for a few hours or overnight should make the labels easier to peel off.  You'll also have to remove any glue that remains from the label. After a soak in hot, soapy water, you can usually scrape the glue off without much ado. A tool like a putty knife, wallpaper scraper, or an unwanted credit card can help. If your bottles have labels that appear painted, like Corona or Belvedere bottles, you can melt your bottle with these still in place. However, after melting, those labels will be permanently melted to your bottle. Kilns can become dirty over time, collecting dust and bits of debris from other projects. This dirtiness can have a negative impact on your kiln's heating elements and can severely shorten the working life of your kiln. To prevent an expensive and unnecessary cost to yourself, before you use your kiln you should thoroughly clean it according to the manual's instructions. While you're cleaning you'll have a perfect chance to give your kiln a quick safety inspection. Tighten any screws that seem loose, remove any flammable material from around your kiln, and verify that all kiln equipment is in good working order. To guarantee your kiln is running as desired, you should consider giving your kiln a test run. You should always use the testing materials and procedure recommended by your manual, but generally, you can test your kiln with a 04 self-supporting Witness Cone. Place one of these on each shelf about 2 inches (5 cm) away from the kiln wall. Then you should:  Set your kiln to run the appropriate test setting, which will be a medium speed 04 ConeFire program if you are using an 04 cone. Allow the program to run for the complete time indicated. After the program has run and your kiln sufficiently cooled, take a look at your cones or testing material. If using a Witness Cone, you should notice a 20° bend or greater in the cone, with no cones hanging lower than the shelf. If you used other testing materials, check your manual to learn how to understand the results of your test. If after running the ConeFire program none of your cones have bent, this may be an indication that your heating element or a relay may have decayed. In this case, you may need to call a professional, like a kiln technician, to get your kiln back in working order. If you don't protect the surfaces your melted glass is going to come in contact with, your glass will fuse to those surfaces. An application of kiln wash or glass separator on your shelf and mold will prevent the glass from sticking to either of these. An alternative you might use in place of a kiln wash is special kiln resistant paper, like thin-fire or fiber paper. These will also prevent your glass from melting to your kiln or molds.

Summary:
Collect and clean your old glass bottles. Clean your kiln. Test your kiln. Prepare your mold and shelf, if necessary.