To survive any length of time in this modpack, you will need to get started fairly quickly. Some tips here will be your best chance for survival.
Your first stepEditLike Vanilla Minecraft, the first thing you're going to need is wood. Find the nearest tree, regardless of height, and chop down the bottom block with your axe. The tree will collapse in logs and saplings. Use these for your crafting table and basic materials for building. Now, equipped with your pickaxe, get as much cobblestone as possible for a sturdier house. Building a house isn't your only option however, feel free to live underground, or in a cave, or underwater. Where ever fits your playing style. For now, we'll use a basic house. Have a living space before nightfall and, if at all possible, aquire three wool blocks or twelve string. Do not risk being out at night for this endeavor. Monsters will attack you.
Your second dayEdit
Now, go back outside of your house and feel free to clear up any remaining monsters with your sword. Avoid boss monsters and named monsters. At the moment, you are not strong enough to face them. With the nearby area cleared, take a stroll around the nearby chunks and mine any coal, iron, or copper. You're looking for a village. Villages provide you with wheat, grapes, carrots, potatoes, wood, stone, Tinker's Construct materials, stations, and patterns. Do not live in a village. This pack includes zombie raids whenever you're nearby. With the special mobs mod, you are almost powerless against raids. Take what you can get and leave. If you do not find a village, fear not. Mining will supply you with more than the village could.
Return to your house and start a small mine. Mine downwards, avoiding caves at all costs. Mine to level 11, ground level. Start mining straight in front of you, again turning at caves. Place torches every twelve blocks to avoid monsters spawning behind you. Mine everything possible and return to the surface once you have a full inventory, you're out of torches, or your pickaxe has broken. Using the cobblestone you no doubt acquired, create a furnace or two and start smelting with any coal you had found.