This could be a REALLY long answer, but the two main things I'd suggest to start are making a plan and putting together a budget. The reality is that without these two things, you're going to have a tough time achieving a successful release. You'll need a budget to accommodate for things like: putting on a killer release show, hiring a publicist (remember they start 8-weeks in advance of the album's release date), and getting together some exclusive merch as well as possibly touring.
When it comes to planning, you want to sit down and really get clear on how you want the unveiling of your EP to look and write everything out that needs to be done. You'll probably find that once you start writing, it just comes naturally. From there, it may look a little overwhelming so you'll start to break it down into smaller, more manageable goals that you can spread out over the coming months and weeks.
For example, if part of your plan is to tour for a week after the release, you know you need to begin to map out the route, contact venues, contact bands in the area that you can play with, and put together posters. From there you can break those down into more manageable goals. For instance, maybe on week one, you map out the route and contact bands, then week two you contact venues, then once all that is set by weeks three or four you put together posters.
Or, maybe you're trying to put together a comprehensive social media plan to boost your following and get fans engaged. So you break that down and know during week one you need to start putting together some graphics with cool lyrics or teaser photos from the album on them to share, and planning out other content. Then you know by week three you need to start posting and networking in groups and in person to start to grow your social media numbers, and by week four you know you should be in the groove of posting every day, maybe even setting aside one or two days to schedule out content in advance. Obviously all of this will change depending on who you are and your specific goals, but hopefully these examples get the ideas flowing.
Promoting your EP is a full-time job if you go the DIY route, or even if you hire help, but the fact that you're asking this means you're ready and willing to work hard and do what it takes to make it happen. You're going to do great!