So once you've identified the places in your locality that might hold the energies of the earth a little closer to the surface so to speak, the next thing you need to do it visit them. Don't set out to do them all in a day - show the spirits of the place your respect by taking your time and not rushing.
Spend some time in each of these places and try to 'feel' them. You might do this by meditating, or you might do this by lowering your energy into the ground, or you might simply open yourself up to the place. Does each place feel different? How easy is it to feel the essence of each place - are some places easier than others? Which places feel special? See what feelings and images come to you in each of these places and slowly start to build up a connection with the land around you.
Once you've done this identify one, or possibly two, places where you think you can work with the energies present. Alternatively if you feel like your relationship with the land is really coming along, or if getting to other special places is difficult, you can start the next step in your own back garden. If you are planning on working your spirituality in your garden this is as good a time as any to start - just make sure you've got the hang of sensing the energy in the Earth first (this is why I have suggested you start off feeling the energy of special sites first - because for a beginner the land's energy is going to be easier to sense in these places).
Chose your site and find a place within it to leave offerings. I'm not suggesting anything elaborate - infact if your chosen place is the middle of a public park then I suggest that you keep things as simple and unobtrusive as possible. Keep in mind that this is not an alter to a Deity, it is a place to connect to the land and leave the spirits that possess it offerings. Maybe you'll opt for a pretty plate, or a shallow bowl if you're working in your garden, or possibly a wooden tray. Maybe you'll decide to simply draw a circle on the ground, where ever you are. Give it some thought and decide what seems appropriate to you.
As to what to offer? Try some wild bird seed, or a libation of water, some flower petals, or even a strand of your own hair. I prefer to keep things natural, but if you're working in your own garden and you want to offer statues or carvings and such like then that is fine too. The key thing here is that whatever you offer it should be from the heart.
Just let the land get to know you a bit, visit regularly and try to make it known that you are listening.