Sure! I think that having fun learning while trying things out yourself is the best way, but I can already give you a few pointers! You should use "layers" in Gimp in order to integrate pony vectors with the environment (lookup a tutorial on YouTube if you need help with that). A quick tip I could give you is this: select the area around the pony that you want to have visible in front of them (like grass or ground), copy the area and turn it into a new layer, place the layer of the pony inbetween that new layer and the layer of the background, then edit the top layer and remove the unwanted parts so that the grass appears realistically in front of the view! There are many ways you can achieve that editing part: color-selecting then removing, eraser, free selection then removing (zoom in very closely in order to do meticulous work)... It takes time, but it works!
You can find some on YouTube, search for example for "Gimp basics tutorial layers" or something like that, you should find something easily enough ^^ Or, you could just try to figure things out while dabbling with the software, it's fun too!
Hey there, that Diamond Tiara piece you featured will sadly have to be taken down due to a conflict over the cover art. I have found a replacement piece of art, and would like to make sure that the features on the various sites will remain in tact. I will send a link to the reuploaded version once I'm done.