On the options, Nepenthe is more talking along the lines (without putting words in his mouth) 2 and 3.

2 is something that is important for all PK with nearly all classes. You can pretty much always catch someone doing this, however classes such as rangers/thieves/assassins are going to have an easier time with this than most. An invoker is going to need to rely on seeing this with ranking groups. In a solo PK contest you're more than likely going to be able to just survive doing #3.

Now, with #3, this is just a suggestion. The key, as always, is to make your opponent get to 0 hp before you do. Since you will defend like a slab of wed noodles at rank 15-35, the goal is to either make their hits hurt less (damage reduction) or to not get hit as much. So, since dam redux is a story for another thread/post, you're looking at getting a charmie.

Here are important charmie thoughts:

Experiment with different mercs/constructs. Different ones do different things. Some have a lot of health. Some do a lot of damage. Some dirt and disarm. Some bash and trip. Some do all of those things. Find the ones that work for the situation you need.

Common tactics with charmies if you want them to tank:
Cast a one-round lag spell on opponent, type order all rescue PLAYERNAME. This rescuing will lag YOU, so as an invoker, make sure you are not auto-assisting.

Cast one-round lag spell on opponent, flee/return so that your charmie tanks for you without lagging yourself. This is hit-or-miss as often your charmie will flee the moment you leave the room. Timing this right is the mark of someone who knows what they are doing. Experiment with this on mobs.

I think mercs/charmies are super viable at low ranks. Often they are under-utilized, and you can find a few that are basically like toting around a level 25 warrior with you (he's stupid, but yeah). Remember that you can only purchase mercs and those constructs your level and below (aka you can't get a level 25 one at level 20).

Let me know if you have any more questions.