There are two different basic ways to run giveaway. If you give a good prize away, it will bring people to your website. The alternative is to require some level of participation in your site before they can be entered into the contest.
With the first, you might need something that is as simple as their email address. Maybe you require them to register for your email address. However, there are minimal efforts for participants. The advantage of this method is that many people might enter. You can easily generator the Instagram winner via (It is also known as “gnrateur le gagnant Instagram via https://osortoo.com/fr/blogue/106-la-meilleure-app-pour-choisir-” in the French language).
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The disadvantage is that you have no guarantee that they will provide anything other than a moment of surge in your traffic. You need to work hard to have great content at the same time so they are more likely to survive.
Remember, even if you only collect their email address, it's the right time to offer a subscription to your email address that you must use to promote your site.
With the second method, there are various ways to go. It really depends on the nature of your site. You can require that the entrants write a certain number of posts in your forum. Maybe they need to submit articles or reviews to your site. Perhaps they can go to your site, get a secret word, then enter your store and tell you that word to be included.