Getting a good conversation out of Dialogue app takes about two minutes of setup and no technique at all. Here is what works, based on how people actually use it.
1. Pick a voice, not a picture
Read the personality line and the favourite topics on each profile. A character whose interests overlap with yours will produce better evenings than one you chose purely on a portrait.
2. Write a real first line
"Hi" works, but "I just got home and today was ridiculous" works far better. Give her something to hold on to and the conversation starts three steps ahead.
3. Set the mode if you have one
Say plainly what you want: light talk, a serious conversation, or a scene. The mood selector in the chat form does the same job in one click.
4. Let her ask questions
The most natural threads are the ones where both sides ask. If you only answer, the conversation becomes an interview.
5. Build stories in layers
For roleplay, establish place, time and relationship in the first message. Add one new element per exchange instead of describing everything up front.
6. Come back to the same character
Continuity is the strongest feature here. The fourth conversation with one character is better than the first conversation with four.
7. Say when something is off
If a reply misses the tone, tell her. Characters on Dialogue app adjust to correction quickly and keep the correction for later.
Ready when you are
Pick a character and write the first line.