1. The mean number of fixed points is 1.  This is very elementary.

2. Consider the operation of rotating three values around: $p(i)\to p(j)\to p(k)\to p(i)$. Given a permutation with no fixed points, there are $n^2-O(n)$ rotations that create from it a permutation with exactly one fixed point. Given a permutation with exactly one fixed point, there are $n^2-O(n)$ rotations that create from it a permutation with no fixed points.

3. From (2), the numbers of permutations with 0 and 1 fixed points are the same to $O(1/n)$ relative error.  Combining this with (1) shows that the fraction of permutations with no fixed points is at least $\frac13-O(1/n)$.

This is the switching method and it can be used in extremely many circumstances. By continuing to increase the number of fixed points by further switchings, step 1 could be avoided.

Incidentally, [congratulations to Terry and Jean Bourgain][1].


  [1]: http://www.crafoordprize.se/prizesawarded.4.2f692b3510dbfce3396800010039.html