Two examples I come across from time to time:
- Remeber to confirm every step in the Bitsquare software
e.g. a trader makes a fiat payment and forgets to confirm in the software. The fiat money gets transferred and both traders wait unnecessarily
- When you fund trades from an external wallet, use an appropriate fee
You can find out the right fee here, for example: https://bitcoinfees.21.co/
Please add your experiences here.