To continue to expand the knowledgebase of Bow users, I will be posting new expanded tactics, topics and guides in my blog as the Ultimate Guide to Bows: Advanced Tactics (UG2B:AT). Please continue to comment both on the UG2B post and these AT posts topics you want covered, expanded, or to just be heard.
Hunting your First Rathalos
The King of the Skies can be a daunting monster to fight, especially if it is your first time fighting him. He has powerful attacks and stays in the air for extended periods. However, armed with the right knowledge, skills and bow, you will be able to knock the Rathalos off his throne.
You will first encounter 'Los after your defeat Lagiacrus, save Kayamba, and unlock the Ancient Mask. By this time you should have the materials to craft the Boltsender 1; the Uncanny Hide comes from a Gigginox and capturing it or breaking its back will usually result in earning one. The Boltsender is key for 3 reasons: Lightning attribute, Blast arc, and Power coating. 'Los is weak to Lighting after Dragon and between the Boltsender and the Arko Nulo (Y), the Bolt is superior. To enhance the Bolt's power, Ingot Armor is best as it will enhance the Spread shot and Lightning attribute. Mining it is simple; the Volcano, Tundra, and Flooded Forest have all the ores you need. As for equipment, you should bring standard hunting gear, capture gear, 5 Flash Bombs, 20 Empty Phials, 20 Nitroshrooms, and Book of Combo 1&2.
The first fight will take place in the Volcano and 'Los will be waiting in area 8 for a cut scene. He will start off in the air, using a Flash will bring him down to your level. When using the Flash, be sure it will go off in front of his face and that he is not in Rage Mode, or it will not work. On the ground his moves are slow and predictable, staying just off center and aiming for his head will put you in the best spot to deal the damage safely. The only real danger you face is a tail swipe and charge attacks, but both can easily be dodged so you are in no real danger. Once he gets airborne, then you have to be careful. He has 2 main states in the air we will call high and low. High he can do some serious damage as he can strike with a triple aimed fireball attack, swoop down for a poison sting, or circle the area and then swoop down for a trample; all 3 require range so hiding under his shadow may be your safest bet. Low, he will fire 1 or 3 aimed fireballs, or swoop in for a charge. Making him flinch in the air will do more damage and put him back on the ground; that is why when he is in low hover, drop a couple of Blast shots in the center of his back to hit both is legs and back for the best flinch chance. Once he drops out of the air, keep the Blasts going to build back the flinch; you can get him in a flinch lock for quite a few seconds with this method, allowing you to really dish out some hurt. After about 50 or so Power shots, 'Los will be hurt bad and probably limping, so ready the capture gear and let him fly to a new area before deploying the trap. Then all you have to do is finish him off as you see fit.
The loot you get from hunting a 'Los is nice. 'Los Armor for archers ups your Attack (m), Pierce shots, and Fire attributes (with gems). To get the Plate needed to finish the set, you will have to capture, carve his tail, or break his head for a chance. Arko Nulo (R) is the bow that would most complement this set, but with the Attack up as high as it is so early in the game, most Bows will benefit.