There is of course many kind of tactics for the
Lizardmen but the one I´m using is the following:
The lizardmen is a fast army and that is what I think
is it´s advantage against other armies. I often use
this in what i call a running army. The most important
units in this army are those with at least 6 for movement,
Skinks with 2 Kroxigors as leaders, Stegadons,
Cold One Riders, units of Kroxigors and Terradons.
Behind these troops i keep 2 units of Saurus, each 20 men
strong. I do this because of the fact that the faster
units ain´t all that strong. They probably will be
beaten up by stronger infantry. If that happens the
Saurus will be there , probably right timed to deal
with them as Saurus is the strongest of the lizardmen
infantry. This tactics works very well against shooting
armies like High Elves and Wood Elves, and it also has
proved to be good against weaker and medium strong melee
armies like Orcs&Goblins one of the weaker armies and
medium like Dwarfs and Skaven. But once you played
against foes like Chaos warriors and Bretonnian knights
it doesn´t seem to work all that nice does it? You don´t
seem to have chance in fair combat against such elite
troops. As I see it there is only one way to beat these
armies, don´t fight in fair combat. Trie to shoot them
out with stuff that allows no save like Salamanders ,
Banner of wrath and that kind of stuff. And when they
reach you, you must trie to charge them in the flank to
negate their rank bonus and get that critical combat
result bonus.

Another nice strategy which I like is the Slann! strategy.
In this strategy you win by breaking units with your Slann
mage priest (you must use a lev 4). You equip your Slaan with
Blade of Cocacila to feel safe against stuff like Frostblade
or Black gem of Gnar.Make him the Battle standard bearer and
use Battle Banner. Select Grey spells and make sure to get
Bridge of Shadows, Grey wings or The Dark steed. During the
battle you teleport around attacking units from the rear
making them break. You then charge them with terradons that
easily catches them. This is a risky strategy since the Slann
can be beaten by stronger fighters, I know there are few but
things like a Verminlord or a greater deamon can beat him up
pretty badly. He can also be stopped for a while with a few
dispel scrolls and if you don´t gets going quick you may fail.