How can I make Dwarf Fortress easier?

I really think you shouldn't. I know that sounds kind of weird but all of the joy you will every obtain out of that game derives from the fact that its Hard. That's hard with a capital 'H.' Man hard. After playing Dwarf Fortress for a year and a half now Hard is a four letter word to me.

Now, as much as I don't think you should change the game to make it easier (and there are sites that will help you hack it). I will provide you with some resources; an instruction manual, so to speak.

The Utter Newby Tutorial. Gives you much of the basic controls and layout for your fortress.

Cpt. Duck's Video Tutorial. I literally learned DF by watching these videos and copying them perfectly. It took me close to 10 fortresses to get to the end of his first fortress. Well worth it.

DF wiki. Students have textbooks, Priest's have the bible, you have the Dwarf Fortress Wiki. Commit it to memory. Perhaps the most important article found here is this one: Fun.

Finally, there is the story of Boatmurdered. It is what is called a legacy fortress, where a different person played each year. Its incredibly entertaining, even though parts of it read like a "what not to do."

I found one of the easiest ways to simplify the game without hacking or removing many sources of Fun is to lower the population cap. I found that once my fortress grew to 100 dwarves or beyond, I couldn't figure out how to manage all of them and keep them working productive jobs. So instead they all just sat around throwing parties and pestering my productive dwarves. Until you get enough experience to handle a fortress that size, try lowering the cap to 40 or 50 dwarves.

To do this in v0.31.08, edit data/init/d_init.txt and change the value of this line:

[POPULATION_CAP:200]

Note: your actual population may still go above the cap you set, you just stop getting new immigrant waves after you reach or surpass that cap. And apparently births don't respect caps. Also I think (but I haven't tested) that you can change this mid-game if you save and quit first.

You can try editing the game's raw creature sources directly. Search the game's directory for a file (probably called creature_standard.txt) that contains the following line:

[CREATURE:DWARF]

Add the following tags after that line:

[NOPAIN][EXTRAVISION][NOBREATHE][NOSTUN][NONAUSEA][NOBLEED]
[NOEXERT][NO_DIZZINESS][NO_FEVERS][NO_DRINK][NO_EAT][NO_SLEEP][NOFEAR][FIREIMMUNE]

This will make your dwarves immune to most status conditions. Now find these lines:

[BODY_SIZE:0:0:3000] 

[BODY_SIZE:1:168:15000] 

[BODY_SIZE:12:0:60000] 

Add one or two zeroes to the last numbers of each line. This will make your dwarves gigantic and unlikely to be killed by anything.

Delete the creature_standard.raw (not .txt) file, run DF and create a new world. Have fun!