Here's the basics...
Soft caps and level increases
When your player levels, you get a free increase to your position specific attributes. These are usually somewhere from .2 to 1 point, depending on how many attributes get these bonuses. For a LB it's either .25 or .5, in everything but speed, jumping, throwing, punt & kick.. These attributes are important when considering how to build your player. These increases are the same per level, regardless of your current attribute score. At certain points, attributes start to increase in cost to raise (referred to by most as the soft caps). Attributes cost 1 skill point per increase from 1 to ~48 (this is known as the 1st soft cap). From 49 to ~60 it costs 2 skill points per increase (this is known as the 2nd soft cap). The higher that you go, the more and more expensive it gets to raise attributes.
Special abilities
Special ability trees are important, but can easily be used incorrectly. Think of them as the icing on the cake. Attributes are what drive special abilities, so if you don't have good attributes, SAs will be almost worthless. Keep away from SAs until you're about level 20, then slowly start to improve them (I.E. do not totally neglect attributes). SAs put the polish on your player, as well as help determine his primary role.
Slow building vs normal building
Slow building is the process of gaining the most out of your player, at the price of not performing optimally as soon as a normal build player. You basically hold skill points as you level, spending them only once you have enough to soft cap a particular attribute (using training to efficiently build up attributes, freeing up SPs for later on in your career). For example, save SPs for 5 levels, during which time you're training an attribute as much as possible. Instead of spending 5 SP to go from 15-20, you train from 15-20 and for the same price of 5 SP, you now have a 25 in said attribute. Most slow builders train attributes to at least 25 before spending points on them.
FB specific
The blocking attribute isn't as important as you'd think for the FB currently. Blocking helps us hold blocks, but FBs don't need to hold blocks very long typically. I'd suggest soft capping it anyways, since this may change in the future and I'd rather be prepared than sorry. Although, you can get away with saving SP to spend elsewhere (about 25-30 blocking should do the trick).
The key attributes for a blocking FB are strength, agility and speed. other important attributes are blocking and vision. Stamina is important for all players, but I only have ~35 and do fine for the most part. The only real difference between a blocking and rushing FB is that, blocking and carrying should be reversed (higher blocking on a blocking build and higher carrying on a rushing build). SAs are what really make the biggest difference in a FB build. For blocking, you want "lead block" and "pancake" (or strong arm, depending on preference). For a rushing, you want "power thru" and "quick cuts" (dive4yards if you're a featured back).
Feel free to PM me questions for clarification or anything that I didn't cover.
