Authors are required to declare any conflict of interest (COI) that may affect their research and their article. Editors and reviewers are required to declare any COI that may affect their judgement when deciding if a submission is worth publishing and to withdraw from handling such articles. Such COIs include funding, personal relationships, working in competing labs or research, recent collaboration with authors/reviewers/editors, etc.
Examples of conflicts of interest might include the following, although it is not an exhaustive list:
If there are other interests which the reasonable reader might feel have affected your research you may also declare them.
You may find the following useful resources to refer to for more information on Conflict of Interest policies, existing codes of practices and more general good practice in relation to journal publication ethics:
View the Guidelines published on good publication and the Code of Conduct by the Committee of Publication Ethics (COPE).