I was wondering if you could give me advice for meditation.
I'm a meditation teacher among many other things. We have a guide on meditation pinned to the top of this board.
True Meditation & The Most Efficient Methods
People always talk about visions and astral travel, but all I get is darkness.
This is what you need to achieve, so you are doing it right (darkness). That is what meditation is, you need to quiet the mind and focus on one thing only. Once you are able to keep thoughts out for up to 20-30 minutes in a single session, you are ready to use it for other means, such as remote viewing, OBE techniques, accessing the akashic, returning to your higher self, etc. Try and do two sessions at least a day (45 minutes eventually is good, but start with 10-20 minutes).
Some topics online are misconstrued, and not helpful for people. I've found that the word meditation has been thrown around a lot and people have lost the true meaning of it. People think guided meditation is meditating, but it's not. People think seeing visions is meditation, but it's not. Those are other things and should have different labels. Guided is great to target specific issues that need healing and/or to get guidance and communicate with other beings. You can also use it to focus on your ego as the thoughts that come up can relate to aspects of ego, as well as emotional trauma that needs healing.
Visions is a result of long term meditation, (some people are gifted and just get them) which you can use 'guided' meditation to achieve it.
Take twin flames for example, in my opinion, there's no such thing, a twin flame is just a soul mate that you've spent more time with in a relationship via past lives. There's so much rubbish coming out of channeled sources online that the concept was created because of that, but much of the channeled sources are not actually the true source, but lower frequency beings manipulating people.
There is a tone in my head that I've always had and it gets more pronounced in meditation. I know it isn't tinnitus as I've had a test for it.
I do get vivid dreams though and they are sometimes prophetic, though I only realize it once the event starts to happen.
Have you tried focusing just on the tone when meditating? It may be helpful for your meditation, but I do recommend mantras as the first thing to try long term for meditation.