Before doing any kind of evocation you should have a skill set that will enable you to determine how dangerous a spirit is likely to be and how to deal with said spirit. This will include meditation, protective work, spiritual cleansing, divination and ritual work. There aren't any short cuts.
Quite simple especially if your already an empath the emotions it has towards you and the way it feels to you for example if its very negative it may be agressive. Though as many have said if the correct skills for sensing and feeling energies it may seem hard if its very powerfull you can easily feel it though I would take that gamble as for example if its negative it would most likely want to harm you and btw the easies way to learn is by meditating, grounding, and raising and feeling your own energies then you have the option of shielding and such then summon minor, to normal, to more powerfull spirits once you got the hang of it. There also many ways of doing this through evocations, rituals, meditation, etc but yeah thats my advice GL.
Invocation is easier (letting the spirit ride you) is easier than trying to make it appear in a triangle. You start by reading about Ceremonial Magic. Modern books like those by Konstantinos are easy to follow and they explain how to meditate, visualize, perform a ritual. Now if you are talking ghosts, I'd love to hear how you channel them.