I'll add to this over time and once everyone is on the team I'll repost this in the team forum.
How do I build a good player? This is the question most new players need an answer to.
First, read AirMcMVP’s excellent post here:
http://glb2.warriorgeneral.com/game/forum/thread/5245024Edit: Second, read Rob.'s guide:
http://glb2.warriorgeneral.com/game/forum/thread/5236282 Can't believe I forgot about it.

Now, I’m going to delve into some things he didn’t touch on.
If the game was just about Capped Skill Values, everyone would use the Slow Built trait for every build. People don’t. In fact, it is very seldomly used outside of Kickers and Punters. So let's not waste a lot of time using Slow Built for player builds.

GLB2 is a game where you want you player to dominate a single role or play a mix of many roles (so other players can be the specialists). You need a mix of specialists and all-around players to win. So deciding on what role your player is going to have is very important.
After you’ve decided on a role, then comes Attributes and Traits. These determine your Skill Caps AND the SP cost you’ll pay to achieve as many of them as possible that apply to your “role”. This is the stage where you plan the use of your Cap Boosts. Cap Boosts add 5 points to any one skill. Combine all 3 and you can pump one skill 15 points. If you look at Attributes and how they effect Skill Value caps, it’s about at 1:10 ratio. So 3 Cap Boosts = 15 Skill Points = 1.5 Attribute points. The problem is that Cap Boosts only effect one Skill. This is why Cap Boosting is typically used in conjunction with Conditioning/Stamina or Sprinting/Speed. These two Attributes have a high correlation to the cap values of Conditioning and Sprinting, but low correlation to other skills. They are almost pure in that sense. So using slightly lower Attribute values for Stamina and Speed in the initial build phase is an advanced build technique used. A 4 Stamina is really 5.5. A 6 Speed is really 7.5. This frees up an Attribute point to be used in one of the other 4 Attributes that have higher correlations with multiple Skill Value caps.
Your Traits should reinforce your Attribute selection.
Not this: You chose Egotist with a 1 Agility score.
Your Traits should further raise the key Skills you’ll be investing in, while lowering the cost of that investment. They should mimic your Attribute selection.
Are you lowering the cost to invest in a Tech skill and raising its capped skill value while having a 9/10 Agility? That’s how you properly align Attributes with Traits.
Now that you have a new player, how do you spend your SP over time?
The simple answer is build to your Traits. Your Traits lower the effective SP cost (usually) of the skills you wanted to spend a lot of SP on. At least, that’s how you should have picked your Traits. Since you now have these Traits (and they usually cost your team salary, a finite resource), use them. Let me repeat this because it’s the single biggest mistake I see with player building.
BUILD TO YOUR TRAITS.
Oh so you went Egotist? Great. Why are your Physicals so low?
Oh you went Technical Blocker? Excellent. So why is you Run Block Power higher than Run Block Tech?
Oh you took Long Reach? Fantastic but why is your Intercepting skill value 30 points higher than Deflection?
The biggest tip I can give anyone regarding player building is: BUILD TO YOUR TRAITS.
General items:
Conditioning.
The more your player moves from his starting position, the more Conditioning he needs. Don’t skimp on Conditioning. There is a Skill Value PENALTY for having low Energy during a game. Having high Skill Values with Low Conditioning means your player gets worse after every play of the game. By the Second Quarter, you’re hurting your team not helping. So plan on a good amount of Conditioning. Lineman can get away with lower Conditioning than other positions, but need high Toughness skills as an offset. If you’re using Cap Boosts on Conditioning then you might be a little light on Conditioning until the higher levels, but that’s a choice you made for long-term build reasons. Just live with it at Rookie.
Build to your Team or build to your long-term Player Design?
This is an easy question to answer. If you have to deviate from your player’s long-term plan because of your current team, then you’re on the wrong team. Why? Because you and the owner/gm/whoever running the team didn’t communicate well on what “role” your player was built for. If the team doesn’t need your player to play that “role” for whatever reason, then you made a bad choice in joining the team. Don’t find any team. Find the team that wants your player to do exactly what he was intended to do. The more you deviate from this, the more problems it creates. And typically it leads to less fun.