Legally, there is no proper way to resign. By that, I simply mean that external laws have not created a particular method for doing so. Each employer can establish their own preferred method, but even then an employee has the right under the concept of "at will" employment to effect their resignation in they way they see fit.
Only when you have a contract of employment would your method of resignation be restricted, and then it would be restricted to the manner contained in the contract.
In this situation then, your main concern is company policy, particularly company policy concerning the payout of vacation at termination. Federal law doesn't require that and state law will enforce any clearly stated policies on forfeiture. some state don't allow forfeiture (in most states...you didn't list your state and if you want to in a follow up questions, use REPLY).
Every state though will require an employer to pay out in accordance with their own terms, so the best thing to do here is determine if the company written handbook or policy requires a specific form of notice and a specific period of notice.
If not and you are free to do things as you wish, it is still BEST (not required) to draft a letter which very briefly states that you resign your employment, and then give a final date of anticipated work. Legally, they don't have to keep you through that notice period though. Notice of resignation is technically immediate, with an offer of continued employment through a certain date. The employer can accept all or a portion of that offered work period, or none of it, and that would not convert this from a resignation to a termination.
The IRA is protected by ERISA law and has to be turned over for rollover into an appropriate fund, if it is not already in an appropriate fund. Your vacation would also have to be paid, in accordance with their policy, in your last paycheck.