Of course, it is highly recommended to start barefooting on smooth surfaces. They are very enjoyable. Take your time when walking and feel all the tactile stimulations and especially the ground’s temperature. You will be very surprised of the variety of textures and feelings. A good way to improve is to walk barefoot as often as possible, especially at home. When it is not possible, use flip flops because, at least, you will train your feet to ambient temperature. Progressively, your soles will change into a soft leather (skin very different from the heel) and you will be able to walk on more surfaces and more places. Usually, it takes less than 10 walks (10 to 30 minutes each ) on the pavement to note some change. Don’t worry, you will not lose your sensitivity ! You will become more tolerant to puncture and temperature.
At this stage, it is better to walk on ground with a strong texture to strengthen foot and sole muscles. You will further improve if you practice regularly. After a while, you can be barefoot anytime whatever the weather is.
The more you practice the longer you can walk. And one day, you will be surprised of your own new physical skills: walking on fire, glass or thorn is not of a great difficulty for barefooters. Far from being magic, this kind of practice is the result of training.
Learn to feel the earth: at the beginning you might be overwhelmed by incredible feelings, and then, with training and experience you will learn to predict enjoyable grounds before walking on them.
As any sport, a too intensive pratice without warm up is dangerous.
Set a goal based on time rather than on distance. Do not overwhelm yourself or the way back may be nasty (unprepared feet can be painful in a few minutes). If you practice 15 minutes twice a week, and keep on barefooting at home, very quickly you will feel that you become stronger. There is no limit if you are trained but at the beginning take your time and learn : it is not realistic to prepare a walk around the world after only a week of barefooting ! At the beginning, the main problem is that some specific muscles of your feet and heels/legs are not usually exercised. Moreover, the skin is not prepared to walk on a ground like gravel.