In the UK, we tend to be more reticent in asking for things; but we can find it particularly difficult to ask for more money e.g. a pay rise. The chances are that you will already feel that you have done enough to justify a pay rise before one is offered to you. It just tends to work like that. Of course, the longer you continue to perceive your work to be undervalued, the longer it can have a detrimental effect on you, so it's worth knowing how and when to approach this difficult and sensitive matter.
Before taking the big step of asking for a rise, consider your current package against the overall market, what you understand your peers to be earning and whether or not you are receiving just reward for what you are doing. Try to be objective and not base in on the new car you've got your eye on. Also, do not consider that a very-well-done one-off piece of work necessarily justifies a rise; perhaps a bonus is more suited to that situation.
Bosses tend to be busy people (who isn't these days?) and they can easily overlook things. Good people can be taken for granted and sometimes they become the 'willing horse' as it is known throughout that a good job will always get done.
So what can you do? Well, the best time to open negotiations and not feel like you are going in cold, is at the point of a role change or promotion, because remuneration is probably up for discussion in any case and it becomes an ideal opportunity for you to broach the subject of your expectations. You should also consider how regular and how formal performance reviews are conducted, as this is also an ideal opportunity to mention your salary without it appearing to be too out-of-place. If you don't have at least an annual performance review, that's the first thing to bring up in conversation as it will be important to know how well you are doing and how you are valued.
If there is nothing left for you to do other than come out and ask for a rise, then consider your approach. You are more likely to be successful if you are tactful and considerate of others, than if you were to barge right into the room and demand a rise. Work the conversation so that it begins by talking about your role, your value to the organisation and your performance. Ask for feedback and listen actively. If everything suggests that you are a star performer at your current level (which should be backed up with statistics as work goals should be measurable) then you are in a good position. Once you are confident that your manager sees all the good in you that you see in yourself, then it's a matter of asking for a rise or, considering if you might be better off seeking a role elsewhere.
Once you are ready and confident to ask the all-important question, do so respectfully, point out what you have delivered and how it has helped the department. Explain that you are looking to progress within the organisation. If your organisation would like to keep you, because you tick all the right boxes for them, they'll find a way; often with a salary increase to tempt you away from looking elsewhere. If that doesn't work out, the only way you may get paid what you feel you are worth, is with another employer. This is the situation you should be prepared to face if your desire for a pay rise is not met by your current employer.