Squ4rex solution is great, but I have some things I'd like to add.
Getting the SS on level 1 is the best way to give yourself an overall score boost, so I thought I'd contribute the "perfect score" for that level:
Difficulty: Hardcore
Clear Time: 01:58
Damage Dealt: 9040
Times hit by the boss: 0
Upgrade chips: 3/3
Combo: 172
This yields 11,927 points, which is much more helpful than it sounds! Just 2k out of 70k sounds irrelevant, but perfecting this very easy and short level allows you to play more sloppily on the others.
My scores and some minor notes for each level:
Level 1: 11,927 (SS)
Perfect this one as per above.
Level 2: 9,992 (S)
I did this one on normal, with gold in every category but difficulty, as I find this boss too annoying to deal with on hardcore.
Level 3: 9,992 (S)
Also on normal. (Mostly because I think I forgot to go back on it on hardcore.)
Level 4: 9,684 (S)
Normal. This is my least favorite boss in the game so I never bothered nailing it on hardcore.
Level 5: 10,233 (SS)
Back to hardcore mode. I find this level and boss really easy, so it's another good one to get an SS rank.
Level 6: 9,444 (S)
This is on hardcore but I took 3-4 hits from the boss and never bothered to replay it for a higher score.
Level 7: 8,984 (S)
On hardcore again, but I messed up miserably on the boss.
As you can see, as long as you perfect the two easiest levels (IMO), you don't have to try very hard on the others! Check out RAINKINGX1's great video guides for boss tips.