My first bit of advice is try to avoid taking the first job that comes along if you know you will not be happy at it.
Make a list:
1) What sort of career/trade am I genuinely interested in?
This is an all important question if you are thinking long term employment. The next questions will help you realistically evaluate the possibility of pursuing that career.
2) What experience do I have?
3) What are my skill sets?
4) What are my qualifications?
If you find you lack the necessary criteria for your dream career, turn the above three questions into goal statements:
1) In order to qualify I need a degree/diploma. I WILL attain these no matter what.
2) I have none or only some of the required skills. I WILL make time to work on expanding and refining my skill sets.
etc...
As others said, prep is key. Once you have attained all you think you need, put together a good resume/CV (you can google some excellent templates and examples for free) and make sure it conveys confidence. Confidence IMO is THE most important quality an employee can have. If you get a shot at an interview, again - be confident! Do NOT short sell yourself, that is a sure sign of a lack of confidence. Always be prepared to answer difficult questions, ask questions and take notes. Demonstrating to the interviewer that you are prepared and organized tells him/her that is how your work ethic will be, too.
You are in charge of your future, don't let obstacles or people intimidate you no matter how daunting. Backing down from what you ultimately want in life will only leave you stranded with regrets and possibly bitterness. Set your goals, work for them and you will be rewarded for your efforts.
Good luck!