Obviously in a town... Just ask in PM where you'd like to meet up.
I would suggest a higher numbered channel because there are less people in your way (sometimes it can get hard spotting someone in a big crowd in town). It's also less laggier if you have an older computer. Channel 1 usually has more player shops so I would recommend against doing a trade on Channel 1 unless you're both already logged in and doing other things. It seems like Darkon and Flaris towns are the most common places people meet up.
Just make sure you both say your d2jsp names, take screenshots, etc etc.