There are a host of articles on how to survive Day 1. Many of them are quite good but generally they follow the same procedure. My procedure focuses on how to acquire Merlin’s Forge armor, weapons and tools to protect yourself and begin to do whatever you like.

Step Action
0 Be sure your world has “Cheats ON”, and Merlin’s Forge and Finder Compass mods installed. Xaero’s Mini Map is an added plus but not necessary.
 1 Acquire at least 4 logs using your bare hands.
 2 Convert the logs to planks (16 minimum) and use 4 of them to build a crafting table.
 3 On the crafting table, use four planks to make 8 sticks. Now craft one wooden pickaxe and one wooden shovel.
 4 Use the shovel to find stone. Use the pickaxe to mine a dozen or so cobblestone blocks. Create a minimum size hole at least 4x4x4. That will provide plenty of cobblestone and the beginnings of your shelter.
 5 On the crafting table, craft one stone axe and one stone pickaxe.
6 Cut down several trees using your stone axe to gather a dozen or more logs. You’re going to go underground and will need them for a variety of purposes.
7 Break up your crafting table and take it to your shelter hole. Restore the crafting table and build a furnace. If you have enough planks, build one chest.  If there is coal nearby, get as much as you can. If not, burn wood in your furnace to create a few pieces of charcoal. You now have all the raw materials you will need to start safely mining.
8 Make a few torches and light your shelter hole.  Then close yourself in using dirt and cobblestone. You now have protection from hostiles, light and basic mining tools.
9 Use your wood and stone to make several stone pickaxes because they quickly wear out. Make at least 32 torches, you’re going to go long and deep.
10 Start digging stairsteps down to level 12. If you run into caves along the way, close them up immediately because hostiles will spawn in them.  Save all of the coal and iron ore you find along the way. As soon as you have at least 3 iron ore, go back to your shelter, smelt the iron and make an iron pickaxe. Gems and valuable ores will not drop when mined by a stone pickaxe.
11 Go back down to level 12 and start mining laterally until you fine redstone. It is fairly plentiful at level 12 and below. If you don’t have at least 4 iron ore blocks, continue mining until you do.
12 Go back up to your shelter and smelt the iron ore (or bring the crafting table and furnace down with you). Use four iron ore and one redstone to make a Finder Compass. Make an iron pickaxe. Now you can mine gems and valuable ores without wasting a lot of time.
13 Mine initially for gold and iron to make tungsten tools and weapons. Diamonds will enhance these tools and weapons.
14 Smelt the gold and iron and craft them into tungsten armor using the normal recipe shapes. Now you are protected from hostile mobs and have a mighty sword to kill them. If you have diamonds, be sure to upgrade the pants, boots and sword to get improved performance.
15 Now you’re ready to return to the surface (when you tire of mining) and do your own thing. I’d suggest killing a skeleton and taking his arrows. Convert some of your gold to credits and buy arrows from the crafting table. Build a Merlin’s Bow and you’re fully equipped.