Lower level PvE builds for operatives don't really exist since you don't really need to use a skill to kill an enemy. (You don't even need to use skills for Dynastar or Red Sun.) But this is what I would suggest:
-Invest your skill points in heal for beginning levels. (Unless you have access to a lot of stim packs.)
-Invest stat points into Dexterity (Another suggestion would be strength but Dex is preferred. Mixing Stat points is more for PvP in my opinion but it is just my opinion.)
-try not to waste your credits on rare items anywhere from 1-19. (I would not suggest doing this since you didn't mention you want to be a twink. Lvl 20 rare set is quite rare and expensive. Save the credits for Level 25 sets and higher.)
-One way to save credits for lower level is to craft. Level 21 guns are great, if you make it yourself or if you get a good deal. (They are overpriced in stall. Don't waste your credits. the crafting materials needed for the guns are very common.)
-Try not to immediately distribute skill points after each level unless you know what you want for your build.

A good PvE build for operatives before 46 and 50 cap maps was an 8 skill build using Precision, Blur, Amplify Pain, Root, Psychic Lash/Mind Wrack, Lurch, and Flames. Stims are still usable so Heal is not required, but still can be used to save Credits.