A while ago I answered the following question on SearchSoftwareQuality.com's Ask The Software Quality Expert: Questions & Answers:

It's been my experience that only the senior testers I work with do exploratory testing well. Is experience a requirement for exploratory testing?

Here is a clip from my answer:

Experience isn't a requirement for exploratory testing, but certainly, as with anything, experience can help. An "experienced" Java programmer (whatever that means) will (in theory) write better code then a Java programmer out of college. That doesn't mean the Java programmer out of college can't write code -- he can. He just doesn't have the same experience to draw on.

The same is true with exploratory testing. Experience can be good, but it isn't required. Notice I said can be, because the wrong experience can be bad.

You can find the full posting here.

Part of that posting lists the skills and tactics used by exploratory testers. It’s also worth noting that version 1.6 of the list is out and posted on the Satisfice website. It has some stylistic changes to it.