It's got a steep learning curve, no doubt about it. Personally, I found the initial challenge level perfect, in that my failures gave me new ideas I was eager to try rather than frustrating me. But I can see how that won't be the case for everyone.
A few suggestions starting out:
1) Avoid anything higher than a 1-skull mission until you've got a solid band formed. That doesn't guarantee you won't get a nasty fight that kills a bunch of people, but it lessens the chances.
2) If you see an easy group of enemies on the world map, go for it. Especially if there is a fight going on you can join in on. You'll get some XP and loot if you kill even one enemy. You need XP to get going, and anything that lets you get safe XP is important.
3) Formation is probably the most important thing. Keep your guys close and use shieldwalls to your advantage. Everyone using the shieldwall skill gets bonuses for everyone next to them also using that skill, so a full line gets a huge bonus. The same goes for your enemies, so knocking someone out of position can be very powerful. Not only does it break up the line, but anyone who gets moved loses any defensive skills they had up. (Like shieldwall or reposte).
4) Your front line's job is to stay alive and protect the back line. The back line (archers and polearms) are the ones who's job it is to kill. Any damage your frontline guys do is bonus.
5) Get a high damage back-line weapon ASAP. Hunting Bow, Crossbow, Spetum/Pike, any of those. They make a giant difference in how fast you can kill and that translates to fewer injuries/deaths on your end.
6) Early game, don't worry about hording stuff that might be useful later on. If it makes you money now, it's probably worth selling to buy better gear/soldiers. Once you're established you can worry about trophies and the like.