Start by heading to the Eastmarch Imperial Camp after having reported to General Tullius for your recent exploits. Once there, go to Legate Rikke and report in for Duty. She will give you the assignment itself for one of the final battles before the Imperial Legion will march on Windhelm.
Join the men attacking Fort Amol
Fast Travel to the nearest point to the assault location. The men are down the slope .
Join up the with the group of soldiers and this will trigger the attack after a quick talk with Hadvar. They are grouped just off the road nearby the fork a short distance from the Fort. Just after that, the assault will begin.
Follow the Imperial Soldiers as they and you head toward Fort Amol. Like all the other Fort assaults, you will not need to enter the Fort itself. All the enemies forces will be outside the buildings themselves.
Prepare your weapons, spells and armor on the approach. Once there, engage and start breaking in. Start by taking a little time to deal with the archers on the walls to make things a bit easier. After that, charge the barriers set up in front of the Fort's entrance and break them down.
After that, it is time to start working through the forces in the Courtyard. Close distance quickly to avoid getting shot by too many arrows. Heal up as needed as you fight through the Stormcloak Soldiers. Not all the soldiers will be spawned in during your initial assault and the dead bodies will disappear as you fight through the battle. If you want to get the maximum amount of loot, you will need to do your looting while in the midst of the assault.
After you have dealt with most the Soldiers in the courtyard, head up onto the walls and start killing off the archers. This can be reversed if the archers are given you a lot of trouble. Just like in the courtyard, sweep along the wall and its heights to hunt down and find all of the Stormcloak Soldiers.