STR 8
DEX 20(22)
CON 14(16)
INT 14
WIS 8
CHA 8
This is probably the optimal ability score setup, but there's a bit of wiggle room.
Dex 22 is annoying in a build because you'll eventually need Great Dexterity to attain an even number. If you don't feel like min maxing and want a free feat in epics, drop a Dex to 21 and invest some points in strength (quality of life, damage) or wisdom (will saves).
Con 16 is optimal for surviving but if you're a player that likes having a lot of skill points you can keep it at 14 and gift Int to 16 instead.
I would advise that you start with rogue levels, because 4x skill ranks at level one means you get a lot more mileage out of this skilly class.
As far as when to take what, I would do something like this for a 8/6/16 split:
1-3 rogue
4-7 fighter
8-17 shadowdancer
18 fighter
19-20 rogue
21-28 shadowdancer
29 fighter
30 rogue
You definitely want your last fighter level as close to level 30 as possible so you can max out discipline
A rogue level at 30 is a good idea for maxing out UMD and other rogue skills that shadowdancer doesn't have.
Your pre epic feats would look something like this:
1) Expertise
3) Dodge
4) Mobility (fighter)
5) Weapon Focus (fighter)
6) Improved expertise
7) Weapon specialization (fighter)
9) Blind Fight
12) Improved Critical
15) Free feat. Toughness? Skill focus?
18) Iron Will
Some might suggest taking Luck of heroes at level one and pushing your other feats back. This will kind of hurt in terms of leveling up as it's useless against early level mobs, but it's fantastic for PVP.
Without going into full detail on epic feats I'd recommend that you go for blinding speed, epic dodge, epic shadowlord, ESF Discipline and epic weapon focus as absolutely essential.
I'm not one of the master buildsmiths here so I'd be happy if anyone wanted to correct me or add anything. That said, this should be okayish starting advice.