Warcraft 3 Frozen Throne Walkthrough for Night Elf Sentinels:
Chapter 5: Balancing the Scales
Main Quest: Maiev's Distress
Before you do anything else, hotkey Maiev and the sentinels around the base as your second hotkey group. You need to pay attention for when the base is under attack and respond. Money will come in trickles as you find it with Stormrage and the others. It is important to focus fire on enemy attackers to conserve as much money as possible.
Take Stormrage and all his forces to the north, and kill the giant turtle. Head east toward the stairs and you'll be attacked by some myrmidons. Use entangle roots often in this level, as well as tranquility. Your army will be almost invincible while tranquility is active. Save starfall so that tyrande can use it later against a Naga base. Use the druids' healing spells as often as you can to prevent losses in the meantime.
The path is fairly apparent, as there are no real deviations except for some gold coins to the east after your first Naga battle. Grab them along with a scroll of mana/healing to help your army on both fronts. The path will take you toward the northwestern corner of the map and the only optional quest in this chapter.
Optional Quest: Night Elf Fleet
The locations of all three ships are revealed to you. Only one of them is on your way to Maiev, however. There is a ship that Maiev could reach in between attacks that will provide a few reinforcements if you're having troulble, but I honestly doubt you will be. Continue on the path with Stormrage. If you find that you have plenty of troops at Maiev's base, use your funds to start upgrading your troops at the hunter's hall. Later, this will come in handy as it's one step you'll have already completed.
Stormrage and his group will eventually come to a four way intersection. West are some gold coins which you should nab, and south is a ship from the fleet that contains a dryad and two mountain giants. Put the giants in their own group and go back to the four-way and take the eastern path. Keep the mountain giants in front so they can use their taunt. Your druids' rejuvenation will work even better on them.
Further on, there is a Naga base that needs to be put out of commission. Send the giants in first, followed by Tyrande who should use Star Fall as close to the center as she can get. Stormrage can then use tranquility to make your troops very hard to kill while you finish off the buildings.
Now that Maiev and Malfurion's groups are together, you will want to move your spirit tree to the spot where the Naga base was. You can entangle the gold mine here and work on building up your army. You will want four ballistas, and two full attack groups to assault the naga base. The time in between battles can be used to wait on Starfall to cool down.
When you finally assault the Naga main base, do like you did before and use tranquility and Starfall to make things easier. There are two halves to the base. When both are down, the mission is complete.