The Padma Purana recommends: somehow or other always think of Visnu, without forgetting Him under any circumstances. Actually this is the most basic of all regulative principles.

It doesn’t matter whether one is a beginner — a brahmacari — or is very advanced — a sannyasi. The principle of remembering the Supreme Personality of Godhead constantly and not forgetting Him it any moment is meant to be followed by everyone without fail.

If this injunction is followed, then all other rules and regulations will automatically fall into line. All other rules and regulations should be treated as assistants or servants to this one basic principle.

(From “The Nectar of Devotion,” by Srila Prabhupada)