Day 1
Raider has a pretty easy time clearing most content, but he does suffer from the fact that his animations tend to take quite a while. Get level 2 and find a Church to path towards. While going there, clear any Forts, Encampments, or Cathedrals and kill the bosses. This should net you enough runes to be a minimum of level 6-8. If you have time left, you can pursue some field bosses for their drops and runes to reach a higher level, or if you have found the weapon you want, you can go to a mine to get a Smithing Stone(2) to upgrade your weapon to Epic if it’s a rare weapon.
You can look for Great Hammers, Colossal Swords, Colossal Weapons, and Great Axes. These are the best weapons in general for Raider, so in case you can’t find a listed weapon, look in these weapon categories.
Day 2
Now we want to look at the map. If we had Noklateo or the Crater spawn, we would want to head there and get the reward. Both net quite a bit of runes but take a while to clear, meaning it's handy to take all day. Otherwise, go to the Central Castle and check if it has Crucible Knights or Banished Knights. Trolls are not worth the time, nor the agony it takes to clear them. If the other 2 spawn clear the castle, then the bosses on top and the bottom to net you a ton of runes while hopefully also dropping some great weapons. After you did that and you have time remaining, kill field bosses for their drops and the amount of runes they drop.
Hopefully, you will be at a minimum level 13 after that and prepared for the boss.
Day 3
This guide is made for fighting Libra, so here are some tips to help in the fight.
Libra is a very chaotic and fast-paced fight, which means that you tend to struggle hitting charged attacks on certain occasions. Libra has 3 attacks on phase 1; He will spawn a sigil under you, which detonates after a short delay, he will spawn a sigil in front of him, shooting madness projectiles, and he can teleport towards a player, which will then detonate 3 sigils around him after a short delay.
He will transition to phase 2 after reaching around 70% HP. He will start to meditate, spawning sigils around him. You need to destroy this to stop his chanting. Every time he does this, meditate more sigils will spawn, with some spawning in the air, meaning if you don’t have a bow, you cannot hit them.
If he finishes the chant, he will become empowered for a while. During this, he will triple all of his sigils and projectiles, making it very hard to dodge. He tends to teleport more, too, during this, so watch out for that. He ends his empowerment with a chant that does a huge AOE madness damage, which can only be stopped by staggering him. Your ultimate ability is great for this.
If he gets interrupted during his meditation, he will be enraged instead. He gets more melee attacks during this and becomes a lot more aggressive instead, but all of his attacks also become telegraphed, making it easier to dodge. He will repeat this until the fight is over.