Well I have a few peices of advice.
First. Try and get 15 Posts, that will allow you to put images in your posts and thread.
Next. Include all info on your Pokemon EXAMPLE Including only the bolded text, as the unbolded is for explination to you :
Shiny Ralts (Shows if it's shiny and the species)
(F) (Gender) Modest (Nature) UT (Untouched, also BT Barely touched T touched NS not sure)
Level 1 (Level of course! :P)
Rules on a nice thread
1. Hacks wont help your thread at all Do NOT trade them under any circumstances.
2. Grammer and Spelling is really important to attract people to trade.
3. CAPITALS. Always use them in the correct places.
4. Always be nice to your customers. Don't rush them, or harass them. Don't get angry. If you don't like an offer reject them nicely.
5. If lists get too long, try using spoilers.
6. Try Bolding sections of your thread, to make it easier to navigate. EXAMPLE :
Shinies
Shiny Budew
(M) Mild UT
Level 4
Legendary
Cresselia
(F) Calm UT
Level 60
Of course all of this is just personal prefference. You can lay out your info. however suits you.
Good luck! ^^