Well, for what it's worth, I took the test twice, but only ever practiced for the second test, about three years later.
In my practices (self-administered), I was pretty systematic. My first practice came out like my first official, cold LSAT. But every week that I did another practice, it went up 2 or 3 points. The test itself continued that trend, and was up a good three points on my most recent practice to that point.
And while that was the continuation of trendline, it was certainly a nice surprise.