Without more information on what is going wrong it is hard to assist, but some steps below might help.

1. Get away from light sources if possible as on longer exposure this will make the milky way almost impossible to see clearly.
2. Set your exposure length based on your focal length and rule of 500. So if you setting 18mm FL then 500/18 = 27.7 so set your exposure length around 25s. This should stop star trailing. if you use 55mm then you will only be able to get 8s or so before star trailing comes in
3. Find the sweet spot on your lens for aperture, the widest is not normally the best for astrophotography, so if you have f2.8 then maybe set around f4. (experiment here to find sharpest).
4. Set your iso around 3200, but again experiment as based on other light sources you might need to lower this.
5. Remember that 99% of the time, the photograph you see at the end of it will show very little milky way. This does not mean that it's not there, but just that you need to manipulate in Lightroom (or other prog) to bring the detail out.
6. Focus is very important to get any detail. use your viewfinder and zoom in to achieve good focus and then take test shot and zoom in to confirm. You can also use things like sharpstar filter to get perfect focus etc

For basic milky way shot, i normally set 16mm, f4, ISO3200, 25s with my 5DMkIII 16-35mmf2.8 and then take a few test shots and can adjust if any issues with amount of light.

Hope that helps get you started.