First of all, you will have to ask yourself what your driving force is. Why you want to learn that particular subject and will it have any effect on your life? This is very important as you should be clear about your goal.
Prepare yourself for self-teaching. One thing most people do not know is that they already are a self-teacher. Same is the case with you so you should try it with one of your interests. If you are a big fan of cricket, start following the game passionately, do not miss important matches, search trivial about teams and players. After some time, you will realise that this exercise has yielded amazing results.
Be consistent, make a routine and stick with that schedule. You should spare sufficient amount of time to study about your subject. It is always better if you have a place where nothing is distracting you.
Next step is to find the right source of knowledge. You may go for libraries, audio and video tools but the internet has become one of the biggest sources nowadays. All you need is to put your query in Google’s search bar and hundreds of pages will be in front of you. You may take help from people who have been through this process.
You should know how to scrutinise the available data as it is all about keeping the right and useful information.
Remember, self-teaching is just a two-step process. First is to observe and then comes to absorb. Just check whether you have learned anything or not. Apply this knowledge to your daily life.