I had been told that the L came first as a means to combat sexism/misogyny. That way, the L put women/females first.
I had been in the habit of just putting the letters in alphabetic order, with the B first and the T last. Originally, it was to put bisexuals first, as it had been my experience that bis were often disregarded by gays and straights alike. Now, I still keep things in alphabetic order, but it's so that I end up bracketing the group, as it were, since I'm bi and trans.
But, that's just my $0.02.