Every ESP will give you tools to create an opt-in form for your site. Generally speaking, the less information you ask for (at this initial stage, at least), the better. The more information you ask for, the less likely your prospect is to complete the process. You’ll obviously need to ask for an email address, and I also highly recommended that you ask for a first name so you can personalize your emails. However, asking for any information beyond these two fields can decrease conversion rates significantly without adding much valuable data.
The key here is to ask regularly rather than just once or twice. Most of your followers only see a fraction of your posts, and you should be getting new followers every day, so it makes sense to request subscriptions at regular intervals. If you can offer some sort of incentive or even just promise exclusive content within your emails, that helps too.