To start you'll need a pattern you like. Look in the evening/bridal section for something that is princess seamed and has an appealing back. It's okay if it's for woven fabrics, I will discuss how to fit the pattern for stretch fabrics in the next section. It's better to avoid sleeves if you can at first, but you can do sleeves if you know how to change the sleeve cap on the pattern so it will not ride up when you raise your arms. Kwik Sew has a good book on swimwear/activewear that is an excellent resource for working with stretch fabrics.

Some pattern suggestions:

Burda
7879 - an actual dancesport ballgown!  I've not actually seen this pattern in person, but it looks very good for someone making a gown for the first time.  Simplicity also has dancesport ballgown pattern, but it doesn't look at all as nice as this one.

Kwik Sew
2514 - I've been using this pattern for years as the basis for a princess-seamed dress.

Style (Simplicity)
9033 - basic princess-seamed dress
9218 - interesting back variations that can be grafted onto 9033
8049 - more back variations to be added to 9033

McCalls
3010 - dress with overskirt (requires a lot of modifications, but still pretty)

Butterick
9360 - "keyhole" shirt pattern that can be extended into a 4-panel dress