Dungeons
Under nearly every island there will be a dungeon which you can explore to find large amounts of gold. Be careful though as they are dangerous places filled with strong enemies, flooded rooms and tall descents. You will also find the occasional animal in dungeons that needs to be resuced, if you decide to save it the animal will become your pet.
Storage
Remember that you can visit your world with any other character you create so storing resources in a central area for all your characters to access is very useful.
Crafting Benches
It is important that you upgrade your crafting benches whenever possible as doing so will allow you to access new recipes for items as well as new blocks that you can use for your base.
Ward Of Protection
Once you have built your base you may want to consider crafting a Ward Of Protection to place around it to protect it from unwanted beasts.
Map
Use your map to help you locate the islands that have the items you need to upgrade.
Arcane Compass
You can save time searching for the portals by using the Arcane Compass. By watching the animation when you use the Arcane Compass you will be able to see the direction of the portal, how far away it is and whether it is above or below you.