"The Wretched Queen is Dead"

After you have killed the Wretched Queen, your objectives in The Fallen Star quest update to as follows:
Use the Old Ruins Waypoint
Talk to Captain Rumford in New Tristram

The journal provides an additional hint:
Use the Old Ruins Waypoint to return to New Tristram and talk to Captain Rumford.

You should see the waypoint blinking and marked in blue on your minimap, a little to the east of the location of the Wrethced Queen battle. But before heading there, you should keep exploring the ruins for more loot, and also to battle any remaining monsters for more experience. There will be a tough battle against a very powerful boss, the Skeleton King, towards the end of the act. So you want to gain as much experience as you can and level up as far as you can before that boss encounter.

Specifically, a bit southwest of Old Ruins Waypoint, there is a sign that says "Griswold's Fine Weapons" (Note that this is just a sign, you cannot pick up the sign itself). Enter through the arch near the sign to go into the ruined shop. Locate a weapon rack and loot it to receive a weapon, for me it was a Masterwork Short Sword. Also loot any Dead Tristram Militia bodies nearby for more stuff. Watch for Walking Corpses and Crawling Torsos and other undead monsters along the way.

When you come across entrances to Dark Cellars, go in and explore them. They will have yet more items for you to find, as well as a monster called a "Treasure Bandit", an impish Demon which you can shoot repeatedly to make it drop gold and treasure for you. Also be sure to search chests, which can include rare and magic items such as one I found, Scouting Cloth Pants. Search bodies of dead villagers for more gold coins.

After picking up enough gold, you will receive the following achievement:

Scavenger
Pickup 500 gold.

After you are done exploring the Old Ruins, it is time to proceed to the waypoint, which is in the Northeast section of the ruins. Waypoints allow you to instantly travel between certain locations you have been to already, so that you do not have to travel by foot all the way again. Step on the waypoint, and a destinations menu appears. Choose your destination. Left click on a waypoint to travel to that location. Waypoints with a Chalice are near a quest objective. The waypoint menu also shows your current location.



Your menu should look like this:

Choose Your Destination
Tristram
New Tristram
Current Location
The Old Ruins

Left click on New Tristram, this will make you travel to the town, thus completing the first objective.