Best advice is to grind to blue, turn in for blessings, focusing on one weapon type. Sadly the best blessings show up on the best weapons, and eventually you’ll have to go to orange to get the mk4 blessings.
Also keep and eye on melk, consider him to just be selling blessings. You can also search on builds, see which blessings are worthwile/mandatory. IE, Warp Flurry (faster charge on chained charge attack) is pretty much mandatory on force staves. Soulblaze seems so far to be fairly worthless. (If anyone has a good build on that, feel free to interject.)
On Ogryn, the most important (my opinion) is 'inspiring barrage" which regains toughness via constant fire, and is the only way to get toughness in ranged as Ogryn. (So far as I know of anyway.)
Zealot and Vet are a bit more flexible.