Since the anus and rectum don't produce their own lubrication, finding and using a good quality lubricant for anal play will reduce the chances of damaging the tissue inside the anus and make things slide in and out easier.
Silicone lubricant that is thicker in consistency, has a longer lasting formulation and wont dry up will achieve that relaxing, sensual, anal sensation you desire. A water based lubricant can also achieve these results though you may find yourself applying more lubricant during your experience.
Before attempting anal sex we recommend the use of an anal douche to keep things clean and tidy. Use a condom and most of all relax.