PLAY THE COURSE AS YOU FIND IT
This is the first time that one of the basic principles of golf has been enshrined in a rule.
Rule 8 covers a central principle of the game: “play the course as you find it”. When the player’s ball comes to rest, he or she normally has to accept the conditions affecting the stroke and not improve them before playing the ball.
This Rule restricts what you may do to improve any of the "conditions affecting your stroke" (see Definition for the list of things that are protected).
Actions That Are Not Allowed
Except in the limited ways allowed in Rules 8.1b, c and d, you must not take any of these actions if they improve the conditions affecting your stroke:
Move, bend or break any growing or attached natural object, or immovable obstruction, integral object or boundary object, or tee-marker for the teeing area when playing a ball from that teeing area.
Move a loose impediment or movable obstruction into position (such as to build a stance).
Alter the surface of the ground.
Remove or press down sand or loose soil.
Remove dew, frost or water.
Actions That Are Allowed
In preparing for or making a stroke, you may take any of these actions and there is no penalty even if doing so improves the conditions affecting your stroke:
Fairly search for your ball by taking reasonable actions to find and identify it.
Take reasonable actions to remove loose impediments and movable obstructions.
Take reasonable actions to mark the spot of a ball and to lift and replace your ball.
Ground your club lightly right in front of or right behind your ball (but you cannot do this in a bunker).
Firmly place your feet in taking a stance, including a reasonable amount of digging in with your feet in sand or loose soil.
Fairly take your stance by taking reasonable actions to get to your ball and take your stance. But when doing so you are not entitled to a normal stance or swing and you must use the least intrusive course of action to deal with the particular situation.
Make a stroke or the backswing for a stroke which is then made. But when your ball is in a bunker, touching the sand in the bunker in taking your backswing is not allowed.
On the putting green, remove sand and loose soil and repair damage.
Move a natural object to see if it is loose. But if the object is found to be growing or attached, it must stay attached and be returned as nearly as possible to its original position.
Avoiding Penalty by Restoring Conditions Improved in Breach of the Rule
There are limited instances when you may avoid the penalty by restoring the original conditions before making a stroke. The determination as to whether the improvement has been eliminated will be made by the Committee.
Restoring Conditions Worsened After Ball Came to Rest
If the conditions affecting your stroke are worsened by another player, an animal or an artificial object after your ball has come to rest, you have the ability to restore the original conditions as near as possible. However, you are not allowed to restore the conditions if they were worsened by you, a natural object or by natural forces.
(see Definition "Conditions Affecting the Stroke”).
If you have the R&A app then look at the Interpretations for Rule 8