The difficulty in Horizon: Zero Dawn definitely scales the later into the game you get, but there are very few of the machines that are pushovers. Watchers may be able to be taken out rather easily with an arrow to the eye, but another early machine that you will come across that may give you some trouble is the Sawtooth.
As the name implies, the Sawtooth is based on the saber-toothed cat and definitely has some size on it. There are plenty of Sawtooths around the world of Horizon: Zero Dawn, but you will encounter one pretty early on in your adventure via a mission that has you taking one down.
The first time you take on a Sawtooth, make sure to use your Focus to scan it for weaknesses on its body and of the elemental variety. Make sure you are hiding in tall grass before you attempt to do this however, as you do not want to be seen at all, as it will destroy you pretty quickly.
It is also a good idea to tag its path as well, so you can prepare traps in his pathway. The Tripcaster that you get before this mission can be very helpful. However, what is the most helpful against the Sawtooth are your fire arrows, as the Sawtooth is weak to fire.
Make sure to keep scanning with your focus so that you can see the weak spots on the Sawtooth and then start hitting those with fire arrows. The weak spot on the underside of the Sawtooth is especially vulnerable to fire, so make sure to use Concentration to slow down time and aim for that if you can to gain a huge advantage. Just make sure you aren’t too close or you’ll take damage as well from the explosion that happens from destroying the weak spot on the Sawtooth’s underside with a fire arrow.
If you can manage to stun it with your Tripcaster and then lay into it with some fire arrows, you should be able to take it down before too long. If you need to run, try to get out of its line of sight and back into the tall grass and start the process all over again.