having someone attack you allows you to see where your faults are and you can go in and strategically move your defenses around. also uptop when i was reading i actually will agree with the strategy of the corner bases for levels 13-20, ive had mine in a corner set up since level 10 and i have had very few losses. placing your low level base in the center allows someone to attack you from behind. they can run into the forrest and come out and hit you in your weak area. so just be ready to defend the best and dont be afraid to "scout" out other bases to get your own ideas :)
and I concur with upgrading your radar, do it when you've basically concured your map and slowly upgrade for a more advanced gameplay. you will soon see more and more people that you can play against and attack. plus more Lt Hammerman bases you can take out. which may take a while depending on your level.