There are usually established international conferences in various disciplines and sub-disciplines, which are held regularly every year, or every two, three or four years.
The organizing committees and/or societies behind these conferences are always looking for hosts and locations for future conferences, and usually, this is decided some years in advance.
You need to participate in such conferences in your field and at the appropriate time, place a bid to host the next one or the one after that, depending on how far ahead these are planned. Your bid needs to be serious and usually you need to have a strong academic status in the field to be considered.
Unfortunately, nowadays there are a lot of conferences which as predatory OA journals, are simply organized to make money of those naive enough to participate. Researchers are getting wary of such conferences, and I'd therefore not recommend that you try to establish a "new" conference, but to get involved in conferences with a strong track record.
Number one strategy is to plan at least 3 years ahead. Invite as may top scientists as possible and have some of their names on your organizing committee. Have sufficient funds.