Prepare for Survival

Clear a space of tall grass and get a bunch of Seeds. Use your Hoe to plant those seeds to make a Wheat garden. If you have the Quark mod installed, then you can right-click fully grown Wheat to quickly harvest it and reseed the soil.
Start Mining Stone. Make a Furnace out of Cobblestone to get an achievement. Switch to Stone Pickaxes once your Wooden one breaks.
Chop down some more trees. Use Stone Axes. Oak trees will give you Apples. Collect the Sapplings to replant the trees later.
Use ~~Planks~~ your Wooden Sword as fuel to smelt some Wood into Charcoal. Craft yourself a Stone Sword. (I usually make more Furnaces at this point so I can smelt multiple things at once.)
Make Chests to help store your stuff. Start building your base out of your preferred material if you haven't already.
If you have the Project Red mod installed, then you can craft some Sickles to help you chop down trees.
Search for a nearby cave, and/or just continue mining Coal and Iron.
Get the Bread Achievement by crafting 3 Wheat together to make Bread.