You can check your progress by going trade network stat under the Status page under the system panel. If it's like other achievements however, you may have to progress well beyond the required number for the achievement to unlock.
The simplest way to get progress would be to buy an immediately sell back an item at each station you stop at. Hydrogen fuel tends to be a good choice for this as it is near the top of the commodities list and will only result in a loss of 4-5 credits, depending on system value.
For actually making some actual profit off of doing this, I found the following website EXTREMELY helpful:http://eddb.io/
That site can help for a variety of trade routes, but for this achievement you'll want to avoid trade loops. It should be easy enough to enter the current station you are at and the next station or system you know you're going to in order to start making some serious profit. Sometimes even trading within a single system can net large profits.