Besides the obvious of using a GPS device, you can also find coordinates with online maps such as Google Maps. Each mapping provider might require a slightly different method for looking up a coordinate, but these directions will work with Google Maps. (At least until they change their interface, as often happens with websites.)

1. Go to Google Maps.
2. Search for the location you want the coordinate for. Let's use South Hills Open Space, San Luis Obispo, CA in our example.
3. Let's say I want the latitude and longitude coordinates of the trailhead rather than the center of the park that Google pulls up. I'll double click the location of the trailhead to zoom in. This also centers the map at that location.
4. Continue zooming in further, as necessary, until the location you're interested in is centered.
5. Just above the top of the map, on the left side, there's a link called "Link." Click it.
6. A box will pop up with a section labeled: Paste link in email or IM with the link that is used to paste in email or IM. In this case, it looks like http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=south+hills+open+space,+san+luis+obispo,+ca&sll=35.2685,-120.659534&sspn=0.026209,0.066047&ie=UTF8&hq=South+Hills+Open+Space&hnear=South+Hills+Open+Space,+San+Luis+Obispo,+California+93401&ll=35.262013,-120.655594&spn=0.001583,0.004128&t=h&z=19
7. Don't let the length of the URL scare you off. The only part you're interested in is this: ll=35.262013,-120.655594. This is the latitude (35.262013) and longitude (-120.655594) coordinate of the point in the center of the map.

Important: Don't use the coordinates labeled SLL—it's the coordinates for LL you want to use!