Alas, there's no easy way.
As you know, the various colectivos run various routes around town, charging around 500 pesos (US$1ish) for a ride.
I personally just walked around while I was there, but that's a LOT of walking, especially if you're walking around the bay to Valparaíso.
From various blogs, including "How to get around Valparaíso and Viña del Mar", the common consensus is along the lines of:
Rates are cheap and travel time is often substantially shorter than
traveling by bus, but it can take some luck to crack the code of where
to catch a colectivo and where it will take you.
Of course, some will treat that as part of the adventure, but if you're on a schedule, when you arrive (presumably) at the bus station, ask one of the agents on the counters for where to catch the various ones. They were very helpful when I was there, drawing all sorts of points on a map and explaining bus routes and the like, which I felt a little bad about since we just ended up walking, but hey, there you go. And of course, many Chileans are pretty friendly and likely to help out if you ask them. And you get to practice your Spanish :D