while some people are born a medium, some can train to become one, and some just don't have the ability. not everyone can hear spirits, just as not everyone can sense, smell, or see spirits. also, because you can see spirits, doesn't mean you can see demons or astral beings and vice versa [you can see demons, but you might not be able to see spirits] i'm just saying these things so you don't get too disappointed if all you can do is sense spirits or something.
you should balance your chakra's to have an unobstructed flow of energy in your body. start from the root and work your way up to the crown. different crystals, herbs and items can help you open the easier. try and study each one before balancing them, then balance one a day for 7 days so you can feel the difference each one will make in your life. the day before you start, go about your day and write down everything you feel, if you feel nervous, if you talked a lot, got a sudden headache and so on.
mediumship comes from your sixth senses [psychic abilities] so you should look into difference exercises to try and strengthen your premonitions and psychic side. some teas can also help with this, but be sure the herbs aren't poisonous, you aren't allergic, and the tea is suppose to be ingested. some potions [teas] are meant to be smelled, not drunk. while you work on strengthening your abilities, try to also study protections and cleansing to keep safe.
when you wish to communicate, you can try meditating, once in a meditative state, ask questions and listen for an answer, it could be verbal [though it won't sound like your voice] could be a feeling, might also be a sound, like a tapping, or something knocked over. pendulums, skrying mirrors/balls/water, or automatic writing can also be used to speak with them. for each of these methods though, be sure you're in a meditative state.
keep a clear head when dealing with spirits, it's true spirits can and do lie, but you shouldn't instantly conclude it was a spirit that made a sound, or whatever. look for logical answers before spiritual. i know it's hard when you want something to happen, but strengthening your clairvoyant side takes time, and communicating with spirits is a long process, so take your time.
You should develop seeing a ghost but it's not necessary, you could also learn hearing one but that's not necessary either. You just need to develop a skill to communicate and know that it's there, this can be done in a great many ways. But for a definite skill I would suggest learning to banish it from an area immediately, when I say this I don't mean use some spell, those usually take too long, what I'm referring to is using magic without spells or rituals those are usually just to focus your energy. Visualization is also a necessary skill otherwise it's hard to do anything to combat a spirit without a spell which takes too long.
You can't become a medium you have to be born one, and I am going to tell you that being a medium isn't something cool you see in books. Mediums get spirits hounding them all the time wanting things, are more sensitive to sound and can sometimes feel everything a spirit is feeling. It can be kind of depressing.
Ok, well MOST people are in fact born sensitive whether it's psychic a medium or both. However, once we get older, more serious, we lose these abilities because society teaches you to GROW UP and shut off those abilities because some people don't believe in sensitive's and there abilities and some it up as a child's imagination. When I was little I DID have an imagination and make thing's up like any other child however some things were in fact me picking up on spirit's, ghost and energy. Like most I completely lost it when I became an older (7 or so) and didn't regain them until I was 13 almost 14.
I started listening more. Learn to sit in a silent room and really strain your hearing. When you hear noises or voices even if there 'voices in your head' listen to them. Most ghost and spirit's can actually read our minds and communicate with us telepathically. Crazy I know, but if you really watch or listen to mediums they may act like there having full conversations with your deceased loved one while not even talking out load and that's because they actually are!
Learn to meditate. I know this really is one of those thing's that are boring and I tried every other avenue but meditation but believe me, it works. Learn to sit or lay in silence in the dark or at least some place peaceful and relax. Don't think of anything intentionally. Just look with you eyes closed and focus on the light's that go on behind your eyes when there closed. Eventually, images will come to you and some can actually be from the other side. Sometimes they will just gradually come to you and sometimes it's like an image literally pop's in your head. Also, learn to see energy. ghost and spirit's use energy just like us and once you learn to see energy it's only a matter of time before you see them with your naked eye. Energy look's like snow or static on the tv. At first you might not see anything, the trick is to unfocus your eyes.Like your looking at one of those books that has a secret image in it that you have to unfocus your eyes to see it. The first time you see energy it's mind blowing and you may think there's something wrong with your eyesight, but rest assured it's fine. Once you learn this eventually you won't need to unfocus your eye's in fact I've noticed you have to focus them to see said energy. With this sometimes you see people's auras, or there energy and I've been able to see orbs and full figured apparitions with this. A couple of months ago I actually helped my mom see her first orb with her own eyes. I literally pointed towards it and without blinking we watched it float for a minute or so then go into the wall.
Lastly, you need to learn to feel, yes feel. It may seem unnerving but really it's not. You must learn to pick up on the emotion's you get when in a room, or looking at a photo or even talking to a spirit/ghost. This can go from emotional to even physical. If that person had an injury that there trying to tell you about you may feel that injury yourself. It can be painful but usually it's so quick that it's like a piercing it's done as soon as it starts. Feeling the actual energy around you and in you can help as well. It feel's like different vibrations and tingles.
What I'm saying is it's not easy. There is no one thing you can do to become a medium and some can pick up these abilities better then others. It's taken me 4 to 5 years of training these abilities to get where I am and I'm STILL developing them. That's the wonderful thing about developing your senses you can only move forward. I'm only 17 and have defiantly progressed since first starting when I was 13 and I'm still learning! It's like working on your flexibility, you can never be to flexible and can only improve more and more. Good luck, and be patient. It will eventually happen. :)
