The most important avoidance tactic is to avoid continuous contact with nickel. In other words anything which comes into contact with your skin for multiple hours per day should not be nickel or contain nickel – rings, earrings, necklaces, belt buckles, buttons, any other piercings, spectacle frames, etc.
Not everyone will become sensitized to nickel through contact but once you are sensitized it becomes a nickel contact allergy and can last for years or decades.
Wearing an item (watch, earring, other piercings, etc) with a high level of free nickel puts you at greater risk of building up a nickel allergy. The more often you wear the item, again the greater the risk. The worst case being something you never take off (ie you wear it day and night) and has a high level of free nickel.
If you do wear (for example) jewelry which contains nickel and you use a protective coating, be sure to re-apply the coating regularly. All brush-on coatings are temporary and will wear off – it’s essential to re-apply to continue any protection it affords.
A mild rash underneath a watch and/or itching, near a belt buckle or around an earring can be an indication of the start of an allergic reaction. My recommendation is to deal with it while it’s a mild irritation – and before it becomes a serious nickel allergy which gives you problems touching any nickel objects.