Heya! As mentioned above, consistency and making good content is the key; however, I'd not really rely on shorts much. You need to build your subscriber base by using long-form videos than short-form videos here. Short-form videos are indeed good, but the subscribers which you gain from those shorts are not really your active subscribers; more likely, they will just unsubscribe you a few hours after they subscribe to you, and If they don't, they will just stay there and won't interact in your long-form videos, which overall will anyway harm your overall channel.
While I do like to go into depth about this question since this is the first question every newbie asks, we already have a fantastic topic made by Stanley here, so If you have any doubts regarding any topic, ensure that you do your research well in the forums, using the search tool and see If there are any similar topics made in the history or the past and read through it. This will ensure that you don't have to wait for people to answer your questions which are already there, and primarily If you do ask a similar question, you will be redirected to the old post anyway.
Here's the answer to the question you asked in this post -
Ok, so here is the deal. This is the single most asked question not only on this forum... but in the entire world. I'm being dramatic of course, but the problem is that this gets asked so often that the people who have been around for a while are tired of giving the same answers over and over...
Wow! I don't like repeating some stuffs for every newbie However, I would recommend you to post lot of shorts, because thats how you will get subscribers very fast. Upload long videos that are same niche as your short. So, subscribers will know that you upload long videos too. Also, add hooks on every of your video. Its a great way to maintain the watch time.