I've always found there are two ways to ask this:
- Compare your income (and benefits) to the market "going rate" for the position and ask politely to be adjusted to that rate.
In this case, you do market research of the rate of pay for your position in your local area. Be careful of national statistics or using statistics based on a different geographical area - jobs are valued by the availability of the skills in that area and the competition between companies for those skills. This is the approach I used when working for large corporate clients as they like to pay competitively in the market I am in.
- Compare your worth as a value of the income generated by what you do for the company.
This is a trickier one but essential to use if you are with a small to medium-sized company or a large corporate in a distressed industry i.e. oil, gas & mining at the moment - the type of company that is counting the pennies to make sure they are getting best "bang for their buck". This is simply a case of showing (if you can) that the income you generate is worth the salary increase you are asking for. I've found that these types of companies can be inflexible in their ability to adjust pay due to cost constraints, but if you have the numbers to show that your business unit is performing ahead of expectations, you might be able to negotiate a bonus or an increase in salary.
In general though:
Always be polite.
Never make statements you are not prepared to follow-up on with action.
Don't be subservient (i.e. beg) - it's business, not a master-servant relationship.
It's not personal if they say no - it's business.
In a lot of places, it is considered impolite to discuss remuneration and benefits with your colleagues, so be careful of doing that.