I saw the Scalenex signal and I am here. I disagree with what Sun King said. Temple Guard are not
mandatory but Temple Guard are very good, and most of
Lustria-Online agrees with me. 20 is not enough in a 2500 point game. I normally go with 26-30 (I start with 26 then add my left over points as Temple Guard). If you are running something with lots of buffs like th Lore of Light or LIfe you can get away with fewer Temple Guard. If you take a Lore with no little or no buffs like Undeath, Fire, or Death you want a few more Temple Guard.
There are plenty of Lizardmen players that dislike regular Saurus Warriors a lot. I am not one of them, but you cannot win often with ONLY Saurus Warriors, 40 Saurus Warriors is plenty, you probably don't need to buy more unless you like grand armies.
There are
four basic LM army builds: Traditional, Predatory, Skink Cloud, and Monster Mash. I like Traditional best. In a 2500 point Traditional army, I like to have two good sized infantry block, usually ~26 Temple Guard, and ~26 Saurus Warriors. You can also swap a block out for Skroxigor (Skink Cohorts with Kroxigor). If I run without Temple Guard I sometimes take two blocks of Saurus Warriors but I tend to do better with one Core block, one Temple Guard block. After buying your Core block, you'll want some Skink Skirmishers. Javelins and shields are slightly better than blowpipes in most games. I would suggest 2 x 10 as the bare minimum. I like 2 x 13 (13 Skinks need to lose four to generate a panic test). I typically round off my Core with a 20 strong Cohort. They become very powerful for their points cost when occupying a building. I am a minority on the Cohort love though, most LM players take three units of Skirmishers.
Next I would recommend a Scar Veteran cowboy. Unless you are likely to face ethereal troops, you almost can't go wrong with how you equip their magic items if you give them a great weapon. I like the Armor of Destiny best.
You got about 900-1000 points left to buy "electives" with. You get a few big dinosaurs, some Salamanders, a second Scar Veteran, Skink Priests to serve as Arcane Vassal, A Saurus character on foot to join your Temple Guard, a Skink Chief with the Egg of Quango, Chameleon Skinks or flyers to run interference and target war machine or even some Razordons. Basically whatever in the LM army book you like best.
I would advise not to take a Troglodon in a competitive army south of 3500 points. I would advise against taking Swarms in a competitive army of any size unless you know there will be lots of rivers. When taking big dinosaurs: Bastiladons, Stegadons, and/or Carnosaurs, I would advise you take 2+ or zero. One dinosaur is a cannon magnet. Two is target saturation. The Solar Engine is better than the Ark of Sotek for Bastiladons. It's not even close.
Kroxigor (not to be confused with Skroxigor) are great at killing big monsters and chariots but bad at everything else. Razordons are good if you are worried about fast cavalry and warbeasts killing your Skink Skirmishers and Salamanders and not much good at anything else unless boosted with Hand of Glory.
If you decide to run a solo Slann, I suggest taking a Saurus Scar Veteran BSB so the BSB can be closer to your main lines and your Slann doesn't auto-die if he breaks and flees. I also believe with a solo Slann a Skink Priest to serve as arcane vassal goes from useful to nigh mandatory.
Sun King is right, two Slann is a bad idea south of 3500 points. Perhaps not even then. If you want to go with two major casters, I suggest a Slann and Tetto'eko. If you run without a Slann at all, I recommend two Solar Engine Bastiladons and a couple Skink Priests (or just on SC Skink Priest). That's a lot of effective magic that takes relatively little power dice.
I'm not worried that Lustria Online disagrees with me on the Temple Guard, I have played them plenty of times now and they do not work in my meta/style of play. Other than that Scaly only speaks pure truth and is an all around awesome guy 