First, probably the single most important mod of them all, is NEI. That screen on the right you get when you open any inventory? That's NEI, or Not Enough Items. This is likely to be the mod you'll use the most, though it has no items in game. At the bottom of the screen is an area to enter text, which will lower the number of items being shown to the left, effectively searching through them to try and find the relevant ones. Once you find what you are looking for in the right panel (or cycle through the pages until you find it), simply left click on it, and then it will show you the recipe for it, if it can, and clicking on any item in the recipe will give you that items recipe, if it can. A right click will show all of the recipes that an item can be used in. Infinity version seems to have a bunch of other info for some things like ore gen chance, mod drops and dungeon loot chance, which is nice. Though be warned, not all recipes are shown (Thaumcraft, for example, hides almost all of it's recipes because it has a research tree) and it shows every item, including stuff that don't have a recipe. Also, note that some things count as other things. For example, Steel and Refined Iron are counted as the same thing for most recipes, however have different crafting recipes.
Another useful mod is JourneyMap (I think that's the minimap and waypoint mod in Infinity, might be wrong). Press B to create a waypoint at your position, and ctrl+B to open the waypoint control menu, where you can tidy things up (especially the death waypoints) if you need to by deleting and editing waypoints. You can use this to mark your base, and interesting feature you come across while exploring (and you'll likely be doing quite a bit of exploring if you look into things like Mystcraft and Thaumcraft).
First thing to do is mine a load of ore, but don't smelt it except for what you need for the next step.
Next, get a method of ore doubling. There are, off the top of my head, three mods that do this in Infinity (possibly more. Lots of mods like the idea of ore doubling); EnderIO (which I don't know much about tbh), the original ore doubling mod Industrial Craft 2 (IC2), and finally, Thermal Expansion(TE).
Now, what is ore doubling? Well, the standard method most mods do is to grind your ores up into 2 (or more) dust, which then each smelt into one ingot. In other words, you've just doubled the amount of ingots you get from a single ore block.
IC2 is the oldest mod that does this, however, it uses EU as a power system, whereas most mods, as mentioned, use RF. Personally, I prefer Thermal Expansion, as it gives you a small chance of getting some extra dust for other metals, though I will admit to not trying EnderIO.
Now, the important thing to know here is that these machines require power, which means you need to build first a power generating block, then the grinding machine block. In TE, the grinding block is called a Pulveriser. After the Pulveriser, the next thing to get is a powered furnace, and link that up to a burgeoning power grid. Oh, and partly automate the process due to the way Thermal Expansion machines auto place items in the inventories of adjacent block if it can.
Once I have that set up and processing my ores, I usually build a Mining Turtle to grab cheap early automated mining. After that, it's a process of working out where to go next now I have the basics down.
And another thing; while you're exploring the world, you may find these bushes that grow berries (blackberry, Blueberry, raspberry, maloberry) on them. Harvest them, and take them back to your base. Then plant them in rows in a brightly lit area, leaving two spaces above them. Eventually, they'll grow back into a proper bush, and then grow another one on top, and another one on top of that one, and every so often grow a berry that can be harvested by right click. Once you have a bunch of them, you'll have a nice supply of food replenish able food that is quick to harvest. They only satisfy 1/2 a hunger point, but you'll be producing a lot of them.
Another point is that because a large number of mods use RF power, you can get power sources from other mods. My current map I started out using a Survivalists Generator from Extra Utilities, before building a bunch of Solar Panels (the kind that make RF, rather than the EU ones) for the free energy, and when that turned out not to be enough power (a single panel produces only 1RF/tick during the day), I built a Big Reactor reactor, which is really the king of RF generation, and used a block from EnderIO to store the power, while transporting it around using Leadstone Fluxducts from... I can't remember what they're calling it now. Used to be part of Thermal Expansion but they spun it out into a separate mod. And somewhere on my plan is to build a treefarm from Minefactory Reloaded.
You're probably not going to be generating enough power to run those machines at full speed until you tech up. A Pulveriser can use 40RF/tick at max speed, while the Survivalists Generator only generates 5RF/tick. At that early stage you're unlikely to need to run that fast and TE machines store power as it comes in until it has enough, and also can operate at a lower speed if it doesn't have enough power, meaning you don't need to run them at full speed.
Also, while Mining Turtles may seem complicated, the two programs you'll need the most are already "installed" on them. By using the commands "tunnel X" and "excavate X" where X is an integer (or whole number), you'll be able to create 3*2*X (w*h*l) tunnels, or a hole X*X down to bedrock. Place somewhere under or near your base, give it some coal or charcoal for fuel, place a chest to dump the store it's mined directly behind it, type something like "excavate 10", then go and work on some mod, such as Thaumcraft, that requires you to remain in the area while it mines for you. Be warned, however, if the chunk is unloaded, such as if you crash or shutdown, the turtle forgets what it was doing and just sits where it was, requiring you to go get it. It's also lava proof, so it may stop in lava, though the standard tactic is to fill automated mining holes in the ground with water so you get the obsidian.
Another thing to point out is something called multi-block structures. Originally introduced by Railcraft (I believe), a number of mods have since taken it up. These are essentially machines that have to be constructed from more than one block. Thing of them like a chest, but larger. They also may be made up of more than one block. For example, the Big Reactor reactor I have currently is a 3*3*3 structure, the smallest possible. It's made from 21 reactor casing blocks, one fuel rod controller, one fuel rod, one reactor controller, one reactor item input/output, and one power output. (can't remember exact names off the top of my head). They're normally the more advanced things in a mod though.
Remember as well, google and youtube are your friends. But do remember also that mod packs are always evolving, so information out there may not be up to date. For example, Thermal Expansion used to have the itemducts included, and most mod guides will tell you to simply hit it with a wrench until it goes red and supply a redstone signal to extract items, whereas in Infinity, you need to build a basic servo to extract items using itemducts. Youtube has tons of guides on both mod packs and individual blocks within a mod pack.
Also note that this is all my opinion. There are infinite ways to play. You don't even need to touch the tech mods and could instead just play at being a mage, researching using Thaumcraft, and Witchery, Blood Magic and the others. Thaumcraft I believe eventually gets Ore doubling at some point. Also, note how others have been putting forth Tinker Construct as a mod to get into quickly. I personally haven't gotten into it yet on my current map, preferring to use the green sapphire and sapphire, from Project Red for my tools. This is merely a difference of opinion. Tinker Construct is awesome, I've used it before, but in my current game, I don't want to spend the resources or time getting into it and creating the basics.
Hopefully this has helped.
