Make sure your website looks appealing, well-maintained, and reputable. Consider if you would submit to the journal if you came across it.
Are there empty, incomplete, or out of date pages, like "About this Journal"?
Has anything been customized visually? You don't have to customize every aspect of the journal's look and feel, but a little bit can go a long way to making the website feel well maintained.
Think about who you want to submit articles to the journal. Where are they most active?
Social media? Listservs? Community sites? These are places where you can promote your new journal and post a call for submissions.
For the first issue or two, you may want to reach out to individual researchers to ask them to submit to your journal. If you do this, do so very mindfully and carefully. Researchers get many junk emails from non-reputable journals asking them to publish, and you don't want your email to be regarded with suspicion as well.
Clarify that it is a new journal, and this is why you are asking for submissions.
Proofread the email for grammar and spelling to distinguish from spam emails.
DOAJ is the Directory of Open Access Journals. Being indexed here means that any library that includes DOAJ on their database list will also index your journal.
The requirements to be in DOAJ are extensive, which is why it is seen as a high achievement for a journal.