I'm an Elite Explorer and wrote a guide in my sig below.
You need a Detailed Surface scanner and a Advanced Discovery scanner (best) then you have two choices....
Honk and Jump from one side of the galaxy to the other twice or....
Explore each system you jump to and scan the bodies you find... Values range greatly, some people fly to the neutron fields and just scan the neutron stars.
Scan values below, also add 50% BONUS For finding first... So you may just make 100,000 on one Water World!
Stars
Class O, B, A, F, G, K, M, L, T, Y 2,400 - 6,600 CR
Black Hole 38,000 - 50,000 CR
Neutron Star 36,000 - 38,000 CR
White Dwarf 22,600 CR
Wolf-Rayet Star (W) 3,000 - 6,600 CR
Carbon Star 2,400 CR
Protostar - (Herbig Ae/Be, T-Tauri) 2,400 - 3,000 CR
Planets & Moons
Belt Cluster, Planetary Ring 0
Gas Giant Class I 2,200 - 3,800 CR
Gas Giant Class II 7,500 - 12,300 CR
Gas Giant Class III 2,200 - 3,800 CR
Gas Giant Class IV 2,200 - 3,800 CR
Gas Giant Class V 2,200 - 3,800 CR
Rocky and/or Icy Planets 600 - 1,200 CR
High Metal Content Planets 4,100 - 8,500 CR
Terraformable Rocky Planets 30,000 - 31,000 CR
Terraformable High Metal Content Planets 30,000 - 45,000 CR
Terraformable High Metal Content Planets with NA[nb 2] 8,600 - 12,400 CR
Metal-Rich Planets 9,000 - 14,000 CR
Water World 18,000 - 36,000 CR
Terraformable Water World 27,000 - 65,000 CR
Ammonia World 33,000 - 35,000 CR
Earth-like World 54,000 - 62,000 CR