This assumes you already have a well established website or blog, or social following.
The easiest way to get traction quickly when launching a new site is to publish off topic content on your established website. Not only do you want it to be off topic(which will be on topic for the new site), but it's OK to use a clickbait-ish title, some fancy infographic or other image and to make it something valuable that people will want to tell their friends about and link to it. You can even add some honey and mention/link to a few choice blogs, let them know you did, and watch their competition link to your cute or fun new post along with them. The goal, break all the rules here and get backlinks.
Post 30 or so of these snarky but fun and still helpful posts that ooze clickbait on your site over time, perhaps even store them in an "off-topic" folder so as not to completely annoy your regulars. Hopefully the new site will be about a hobby of yours which will personalize you further with your existing site readers, whatever, have fun with this.
Let a year go by after posting them, keep linking to them from social media once a month, heck advertise behind them to get as many eyeballs on them as you can. Goal, backlinks! Do not internally link from within the content to your existing site, that's the ONLY rule.
Now convert.
Having become good and ripe and, hopefully, backlink rich you can set up the new site, template, design etc and prepare it for launch as you normally would. When that's done head over to a tool like Google's search console and look up the keywords that get the most search impressions. Fix the titles using one or more of the top keywords the page is getting views for. Go into the article itself and tone down any silliness, update it to be even more of a helpful resource but keep it similar as much as possible.
Now 301 the lot of those 30+ articles you wrote as off-topic over time to the new domain all at the same time and launch the site. Then do nothing at all. Let the site sit untouched for another 9-12 months. If you did your topic research and focused on article topics and keywords you knew you could rank well for, ie:informational content for informational keywords, you'll be seeing traffic and results happening all on their own after 6 months or so.
Not only will the site have launched with ready content fleshed out but with ready backlinks as well, a year's worth. There was no scrounging around on new social profiles to get an initial kick. your established site did the heavy lifting for you.
Does this even work?
Right now, without fanfare or warning to the public, some extremely massive publishing companies have done exactly this for instant traffic to new domains which are not labeled as belonging to those companies. It's working for them, it will work for you. Your scale will be much smaller, perhaps 1000 backlinks to 30 pages compared to their 20 million backlinks to half a million pages, but the end result is the same. Your content will likely be higher quality as well, it wasn't written as keyword fodder by a contract writer.
Mods: I have discussed this practice, and provided evidence, that it is being done by, and is working for, wall st listed media publishing companies via sticky mail already. If more is needed for you to avoid thinking I'm "defaming" a company(that I haven't mentioned) or that I'm following some conspiracy from a dubious source, contact me and I'll walk you through it all with examples that will, quite honestly, make your jaw drop.
Yes it works, moving content from site A to site B is perfectly fine with search engines, in fact if you have a site A you should never struggle to build a site B(or C and D and E) ever again. It will keep working too because it stops working for small sites some very big companies would get very upset with Google.
