There are all kinds of constraints when you create a character. Most are determined by the GM. Crucially for the character creation process, the gamemaster must determine the Free Packages appropriate to the setting, and the number of Background Factors each player may allocate to his/her character.
The GM should also provide guidance regarding his/her setting, and the sorts of characters suited to it. Players may also wish to collaborate in designing the "party" mix. E.g. a 40s film noire campaign might not work too well if everyone plays a femme fatale.
The key to successful character design is sketching out and then developing a good character concept. A good character concept is distinctive, appropriate, fun to play, and fun to play with.
At this stage, the character concept need be no more than shorthand: "American male; early middle age; world-weary, cynical; former freedom fighter; now runs casino/bar".
You should select a number of Background Factors (subject to your constraints), including one or two Childhood Factors, for your character. These should be listed in the order in which they occurred.
Background Factors both sketch out your character's past life and serve as a rationale for his/her level of competence.
Each Background Factor confers on your character a number of GPs (generation points), Educ (education points), and possibly other benefits such as extra inherent attribute points and special talents.
Allocate 36 points (plus any extra points from background factors) to the character's inherent attributes, which (for human characters) start at 5 and can be raised to a maximum of 12.
Select a free package appropriate to the setting and allocate any discretionary points (usually Familiarities) as desired.
Spend the GPs and Educ on skills and fields appropriate to the character as conceived and in line with his/her background (so far as it has been sketched out).
Note: determining a character's skills and knowledge often helps flesh out more details of his/her background. It's a good idea to think in terms of background when selecting skills and knowledge and vice versa.
Determine the character's age and generally brush up and flesh out the character conception in line with the changes made so far.
Determine the character's Merit Point total for his/her profession. This is best done in consultation with the GM, who may have ideas as to the character's future career.
Fill in the remaining blanks on the character record as appropriate. This basically comprises calculating skill PCSs and other bits and pieces, and making sure no skill has been raised to too high a level.