As others have suggested, riding with others who are a bit faster than you are will help, but only really with speed endurance. Another thing to think about when you want to go faster, is power. Basically, a full training regime will, over time and according to your abilities, build endurance (base miles), then strength (strength endurance eg riding up long hills in a fairly hard gear, maintaining a low cadence, but without 'grinding' the gears), and then power (that explosive burst that let's you pull away from other riders and leave them wondering who lit your rocket).

Riding with others faster than yourself is a good place to start though, and if you are only riding for recreation, then you really don't need to worry about training blocks, what intervals or efforts to do etc. If you're lookihng to race though, the best place to start is to try a few club races, and get yourself a coach so you've got someone who's able to look at your riding objectively and point you in the right directions at the times appropriate for you.

It's okay to self coach, but bear in mind that most riders lack the knowledge and understanding to properly develop their riding a great deal. Yes, you'd see some improvements, but nowhere near what you get with the guidance of a good coach.