This question is inspired by the video essay series "Fantasy Re-Armed" by Shadiversity on YouTube, where Shad explores typical fantasy races and what weapons they and their opponents ought to use.
My lizard men have about the same body mass as a human and the same intelligence. Unlike many fiction lizard men, they walk with their spine horizontal, like most bipedal dinosaurs. Compare to a Pachycephalosaurus, but smaller.
Their teeth, claws, scales or feathers are not powerful enough to serve as weapons nor armour. Their tails are only moderately flexible, not prehensile. Their physical strength is comparable to a human.
One very significant aspect is their posture. Since they don't stand erect, they will be lower and longer than a man of the same mass. One disadvantage is that they cannot form as tight formations as humans since they take up more area. One advantage, however, is that when viewed from the front they are much smaller targets and potentially harder to hit - useful against melee weapons, crossbows and guns. On the other hand, they present a larger target from above, potentially making them more vulnerable to volleys of arrows.
I imagine that the tail provides useful balance that will make them better and faster runners than humans. (That's what tails are for, isn't it?) This might make them better skirmishers (armed with guns or bows and harrying the enemy) where humans make better formations.
Note that the lizard men will not necessarily always be fighting humans. They can also ally with humans and form mixed armies to fight against other lizard men or other humans.
The technology is late medieval or renaissance. Guns exist, but they are only as powerful and reliable as 1500s arquebuses. There exists plate armour that is largely bulletproof, but it is expensive.
The lizard men have quite flexible shoulders and necks. They can, for example, lift a shield above their torso and pull their head back so it's above or behind the shoulders, if need be.
What weapons and tactics should they and their enemies use? What do I need to consider? Do you have any advice?