Because Build Points (BP) have a flat cost, and karma point costs increase with level, I like my characters to start out heavily emphasizing a niche, and then growing more diverse over time.
If your character is combat-focused, agility is important. If you're tech focused, bonuses to logic-linked skills are important. If you're a mage, your drain stat is important.
I generally start with a synergy of some sort. My current character, as an example, is a face / charisma-traditioned magician. Both roles use charisma, so that gives me something to focus on.
Dice Pools
Rather than being so-so at 10 things, I want as many dice as possible in my one, then a second, etc. For charisma, I have a couple options on raising the stat. If I go elf I can have a higher base. Similarly I can raise it with Exceptional Attribute or SURGE. Also by taking Genetic Optimization. Finally, if I can cast spells I can use Improved Attribute (Charisma). Any of these could help me get more dice in my charisma, which would affect both my social skills and my drain soaking. Magic and bio/cyber-ware are the two main ways of increasing your pools without spending a bunch of BP. Hence the adage, anything a mundane can do, and adept can do with +5 dice.
Your dice pool (at least in Missions) is limited to 20 dice or 2*(attribute+ability), whichever is higher. So when I'm going for 21+, I make sure to focus on raising my actual attribute or ability, in addition to bonus dice.
Your maximum attribute score, in turn, is limited by your base. Exceptional Attribute, SURGE, or Genetic Optimization, then, are particularly valuable because they raise the augmented maximum. That said, they're expensive. 20BP of quality, Distinctive style, or essence loss. SURGE in particular is great value, except for the -3 to perception rolls against you from DS.
'Ware
Few characters would not benefit from 1 essence worth of 'ware.
For ware, keep in mind that -.1 essence loses you no more magic/resonance than 1.0. So try to spend in whole points. Also, combine bio and cyber to get at 50% essence discount on whichever is lower. Mathematically, the closer you can get them to even, the more you'll benefit from the discount. So for 1pt of essence, .7 worth of bioware and .6 worth of cyberware would be almost the most you could squeeze into 1 point of essence loss.
Combat
Unless you have a plan for avoiding combat entirely, try to get as many passes as you can, a high dodge pool (especially reaction + bonuses that apply without declaring a dodge action), and high armor.
For armor, use a combination of Form-fitting (which combines with other armor but only encumbers by half), softwoven armor (which reduces the encumbrance of the higher value by your strenth, and SecureTech PPP to balance out ballistic / impact. I look for bonuses like -2 to detecting objects hidden under (long coat) or -4 to perceive the character (ruthenium).
If your character has good combat stats, look for automatic bursts / high damage weapons (combat axe). If you're not, look for something that just has to hit, like stick-n-shock. Grenade launchers (I favor narcoject + DMSO splash grenades) can be the easiest to hit with, but don't forget the Airburst link or people can leave the area before they explode.
Misc
For contacts, I find 6/1 to be the best value. High connection means they do the most for you, and you can scrimp on BP for loyalty if you don't mind paying for their help / increasing loyalty through RP.
There are so many useful positive qualities, I almost always take 35 points, or close to it. But BP are so scarce, I always take 35 negative. Play around with different negative qualities until you find ones that either a) don't slow you down in your niche or b) better yet, you enjoy playing. I like characters who remember to check the news daily, so I play a disproportionate number of characters with Media Junky.
A good rule of thumb is 1BP = 2 Karma. With that in mind, look for ways you can get something at character creation for < 1/2 the karma cost in BP. An attribute of 5, for instance, cost 10 BP instead of 25 karma. A skill at 6 is 4BP instead of 12karma.
Skills are generally the easiest thing to raise with karma, so I assign BP there last, and often have a bunch of ones. Specializations are *AMAZING*, but cost the same amount in Karma they do in BP. Get them shortly after creation, rather than during.
