Character tweaking is a very important part of any PnP/RPG game. The idea is to create a combination of personality and physical attributes that represents your personification in the Fallout setting. The best way to decide how to build your character is through considering advanced ideas about character creation and development.
Race is extremely important. Consider the rules about minimum and maximum skills. A ghoul boxer isn't as obvious a choice as a human or super mutant. Remember that traits such as Bruiser can't raise your strength over the maximum for that race. Each race has favored archetypes, with human being a very level headed race.
Some players greatly enjoy Traits while others find them character hindering. In good spirit you should try to include one trait with your character if you wish to have a tweaked character. To continue using the Bruiser trait, so you lose 2 AP. That +2 to strength will come in handy. It will also make your character more able to break bones. If you are a brawler that's what you want. Each of the archetypes have traits that work well with them. Mixing and matching your traits can make a well-tweaked character.
Your characters statistics will be very crucial to your tweaking. Changing any point just 1 up or 1 down can be the kill, the barter, the wrench turn. Keep in mind that min-maxing will make your character good at what she needs to be good at, while at the same time taking the challenge and roleplay out of your character. Tweaking a character is by no means min-maxing.
Skills are another important tweaker tool. You can customize even more inside of your archetype. Tag skills are very important as well. It is safe to say you should take 2 of the 3 tagged skills that work well with your archetype. Then use the last one to further customize your character. When you are working on your character concept consider some skills to be outside of your characters personality. Chances are a grease monkey isn't also going to excel in first aid and surgery.
Archetypes are the focus of your character. Your archetype usually has a connection to tagged skills and perks you choose as you go through your characters development. A few great examples of archetypes are:
(click for breakdown)
Each of the above mentioned Archetypes are important in their own way to the world of Fallout. What you make as a character is likely your choice, with possible intervention from your GM.