What I like to do is create characters with three or four major skills they plan using frequently (including at least one weapon skill, unless it is a pure mage) and then fill the other skills in with slow levelling skills that any character can make use of, like acrobatics, mercantile, restoration and block.
I don't like efficient levelling because I find it rather boring, but some skills work well as minor skills because they level quickly and contribute towards good attribute bonuses.
Armorer makes a good minor because it leads to endurance boosts. Pay for training to level armor up to 50 so you can repari magic weapons and that will guarantee at least +3 to endurance each level, but you will likely get some +4 or +5 bonuses.
Conjuration and alchemy make good minors because they both level very quickly and lead to intelligence boosts (important if you are a spell caster). Alteration is kind of the same and leads to willpower boosts.
Light and heavy armor work well either as major or minor skills.
Sneak and Security make nice minor skills for melee types because they lead to Agility boosts (important for melee fighters because of the stagger reduction).
Marksman levels slowly, so it is best as a major if the character plans on relying on a bow for more than hunting.