Salary is, and should be, an important part of the discussion during a recruitment process. It's not only a question about terms of financial compensation but also about potential challenges, perks and other key information (such as holiday entitlement) to have before deciding whether to accept a new job.
You can find lots of statistics on market wages just by googling it. Compare your own salary with others in the same profession to get a greater understanding of what is reasonable, in both directions.
Write down what you do, and keep track of your projects. Don't rely on your boss to remember all of your achievements and be prepared to remind him or her of all your new tasks and responsibilities.
If your company is going thru a a rough time financially, it might not be the perfect time to bring up you salary claims. Wait until things are going in the right directions and you will have better odds to negotiate the salary you want.
However, just becauses the financial health is looking good , this doesn't automatically means you will get a raise. And also, even if your companie is not doing so well but you've just reached an impressive milestone or exceeded an important goal, then this could be a convenient occasion to talk about your compensation. If you've earned it, it will probably go your way.
It's important to remember that while your salary is vitally important, it's not everything.
Obviously being well paid is a great aspiration to have, but if you're not happy in your role to begin with then will more money really make that much of a difference? Sometimes it can be more beneficial long-term to take a lower salary in a job that meets your needs in other ways (such as role responsibility or the type of work you will be doing).
We all want to feel that our salary reflects our performance, but when having a salary discussion, coming across as 'money hungry' can actually have more of a negative effect on your chances of getting that pay rise. So, if you do have a salary discussion coming up, then it is best to prepare and make sure that you can justify any increase you're asking for.