One of our greatest tools in life is our intuition. The irony is that so many ignore it or are not aware of it.
What is intuition?
For me, it's a sign post. A road map. Something that tells you if you're headed in the right direction. Something that tells you whether everything is right or not. Something that tells you what to do and what not to do in order to reach the goal you've chosen.
How do I use it?
I don't know what it's like for others, so I can only draw on my own personal experiences here. For me, I find when I'm thinking about a certain course of action, or am doing something, my stomach (in the solar plexus chakra area) will either feel distressed as though something is churning within me. (It's a feeling resembling fear, even if no emotion is attached.) Or I will feel a sense of joy, connectiveness, truth or love.
When it's the former, it means that actions or situation will not suit my purposes. The stronger the feeling, the less I should do something. When it's the latter, it means I should follow the actions or situation, no matter how unlikely or insane it might seem at the time.
People may say to you, when your intuition says something isn't going to work, 'oh, you're being negative!'. Well, no, you're being connected. It's like saying I wish to head north, but we're heading east right now and we'll never reach our goal. 'Oh you're being negative' might convince the person that they should be continuing east, rather than listening to their internal guidance.
If things were obvious, we wouldn't need our intuition, but they rarely are. When we call forth events in our life, we are also given directions, but those directions might seem wrong because they are pointing you in a different path. That's when people ignore them and go in the direction they think, or logic dictates they should. In the end, often things just don't work out quite as expected.
An example of this might be supposing you are at a train station and you need to get to your destination as soon as possible. The train arrives. Your first inclination is to board it, and logic tells you to, but something holds you back. Maybe it's a feeling, maybe it's resistance in your movement, or you might start feelings of stress occur. The thing to watch out for is does it feel right to board this train? You decide not to board it, and 5 minutes later, another train comes. This one happens to be an express train, and will get you there 10 minutes sooner. You didn't have that information, but your higher self did.
There times when it's not always easy to tell what your feelings of intuition are. Fear can be a major interferer. For instance, if your child is home late, the fear of something having happened to him/her will often override your intuitive feelings that al is well. (In which case, I'd recommend the Bach Flower Remedy, Mimulus, for known fears.) Aside from that, I find the best way to distinguish your intuition is to stop trying to work it out, and just put it to the back of your mind and let it seep forth.
Running through options.
Now your intuition might be telling you that a path, situation, person, etc, is wrong, but how do you know what is the right choice? I found the most effective method is to run through options in your mind, and see what 'clicks' into place. You'll know when you've hit the right one, because there's a feeling of 'yes, this is right' go through you.
When messages change...
Sometimes it's just a small thing that might make a difference. Sometimes it's a complete change in direction. Where many people become unstuck is that they will feel that something is right one day, and then next day they will feel the same action is wrong. So they feel they should stick to their original feelings, otherwise, how can they trust anything if they were wrong?
What isn't understood is that your intuition is based on what is happening right now. Things change and people change, and they might change their minds on certain issues, and then change them back later. If you felt something was right, and then felt it wasn't, that's the time to really listen. Trust the moment. All we have is now.
My final thought on this subject is that just because you try and make something feel or be right, it doesn't mean it is. Your intuition can guide you to making it right, but first it's important to acknowledge that things aren't right, right now!
As it is, I've not perfected my understanding of how intuition works. For instance, I can't seem to feel which lift will open when I'm waiting for them. :-) But it does seem to me that the more important something is, the stronger your intuition will cry out to you.