The best advice for someone considering a do it yourself colon cleanse is; don't do it. Unless by do it yourself you mean ordering a system and taking an herbal supplement by yourself every day of course. The safest and most effective method for colon cleansing is to simply find an herbal system, either online or in a vitamin store, and follow then to follow the directions that it will come with.
Of course if you mean do it yourself as in find ingredients and mix up some sort of potion you should reconsider. Colon cleansing is too important to your overall health for you to be attempting to be a modern day medicine man. You wouldn't try to mix up your own penicillin so why would you consider creating your own colon cleanse formula?
Many of the herbal supplements that are available have been improved through years of research. The companies that make herbal colon cleansing agents have strict quality assurance controls and most of them have been doing this for years. There is literally no good reason to attempt a do it yourself colon cleanse method when so many commercially available methods have had proven success.
All natural colon cleansing agents typically use an herb derived from psyllium husk. Psyllium husk is only found in Pakistan and India and is only harvested at certain times of the year. Even if you were to buy psyllium husk someplace there is no guarantee that it will work. In fact there is no guarantee that it is psyllium husk at all. After all how many people can tell one crushed her from the next?
If you wish to obtain the maximum health benefit from a colon cleanse don't try a do it yourself recipe. Find a product that has already helped thousands of other people and order it. This is the safest and, quite frankly, the easiest way to cleanse your colon of harmful toxins.