Note that all of the following methods and forums have their own policies or guidelines. The following is just general advice and you should refer to each separate forum for the precise rules applicable there.
Give discussion a fair chance and don't jump to dispute resolution too quickly. Only after thorough, extensive discussion, if discussions on the talk page aren't going anywhere, ask for help from one of the following.
But don't wait too long after discussion has ceased to ask for dispute resolution as most of the following forums require as a prerequisite talk page discussion which is not only thorough and extensive but which is also recent.
Third opinion
For simple content-related issues between two editors, you may bring your dispute to third opinion to ask for an informal outside opinion. If the dispute continues after, you can bring it to the Dispute resolution noticeboard.
Dispute resolution noticeboard
For complex content-related issues between two or more editors, you may bring your dispute to the informal dispute resolution noticeboard. This is a good place to bring your dispute if you don't know what the next step should be.
Requests for comment
For simple content-related issues where concise proposals have been made on the talk page, you may bring your dispute to the informal requests for comment to have the broader community look at the dispute and make suggestions.
Arbitration
For conduct-related issues that have been through all other avenues, formal arbitration is the last and final resort for conduct. Arbitration issues binding solutions through the form of sanctions.