I guess the best place to start is to state what build your sorc will be.
If your play style is to stand far away from the mobs, then consider a Meteor sorc. If you want to play as a party-helper, then consider an Enchant/Hydra sorc. If you'd rather something fairly uncommon, then consider a Blaze sroc.
For any of the builds, the skill distribution is pretty simple, since you just need to max the main skills the build is named for along with their synergies. Hybrid sorc builds aren't too common or powerful in HU since -%Res (e.g. unique Facet jewels) is plentiful (the challenge is in breaking the immunities).
1) Getting around -80% to enemy fire res is very important by the time you've reached Hell, and about 50% before then is a fine idea. Rubies in your weapon will do most of that if you can find nothing else.
2) Energy Shield works very well with DR/MDR (i.e. diamonds in armor and hat), since EShield diverts damage to mana before the DR/MDR goes into effect (e.g. with 50%ES and 50DR/MDR you lose no HP from 100 damage). You don't need ES for norm, but if you plan to stick with DR/MDR then you'll need it for late NM and Hell.
3) Blaze and Meteor have a damage-per-second effect that stacks, so if you build up their patches of fire before leading monsters to it then the monsters will die very quickly. It would be a good idea to get a tank (party or merc or something) that will lead monsters to the patches of fire and keep them in the patch until they die.
4) The +Fire damage added to attack from Enchant, charms, and items will all add to the "Explosive Arrows" mod on some bows.
5) Read the
FAQ point 3 for quite a bit of information related to items.
If you have more questions, consider searching the forum for them before asking. If you still can't find an answer, then please be very specific. Consider posting your finalized build idea with a question at the end like, "How would you change this". If your question is too broad, then people won't know where to start when answering, so they won't bother.