This problem has different solutions depending on how you want to play.
If you're just looking for the achievement, one solution to your problem is to do whatever missions you want, choosing the side of good, until you get relatively close to your level point. Then go into a town and steal (for minor karmic reduction) or lay waste to entire towns (for major karmic reduction). You can quickly lower your karma this way. Then, once you're neutral, go kill some random creatures until you level.
(If you're looking to steal, a good place to do it is at Dukov's place… he's got stuff everywhere.)
The "nice" thing about this system is that if you stay on the path of "good" the whole time, you can do this at each achievement point: be bad until you get to the right karmic level, level up, get your achievement, and then restore a save to get back to your good self. You can quickly get "good", "neutral", and "evil" achievements for all levels on one playthrough this way.
(I did this, because I don't really enjoy long-term playing as an evil character… but I do like my achievements!)
You could also do this as an evil or neutral character, but it's much easier to quickly drop from "good" down to your new goal, than to work your way up.
If you find that you're close to leveling, and you're at the right karmic level, and don't want to take a chance on changing your Karma by doing a story-type adventure, you can always go wandering looking for random bad people to take out. Going near the Washington Mall can get you some XP fairly quickly, and you can go inside the capitol building and clear out large areas without picking up any Karma, positive or negative.
Parrying requires you to block just as the attack hits, not before it.
Rather than holding O, try pressing O just as the enemy's attack is about to hit, then when the attack is blocked, attack with Square
Best Answer
The main quests as well as the Hunter Trials will award you Skill Points. If I remember correctly, main quests usually give you a Skill Point as a reward. Getting Blazing Suns on all 3 Hunter Trials at a Hunter Trial area will also award you a Skill Point. Additionally, completing Cauldrons and climbing Tallnecks will reward you Skill Points. If you haven't done all of these, you definitely should. From experience, I capped out my Skills by the mid-40s and was still receiving Skill Points from main quests and level ups, despite having nothing to spend them on.
By the end of the game, completing Hunter Trials and Main Quests should award you way more than the required number of Skill Points required to unlock all skills.