Heyo.
It's great to have a long-time reader join. Congrats on getting accepted!
Of course, if you want to write SCPs, make a sandbox page for yourself. Get your stuff reviewed in the IRC chat and/or the drafts forums before you post to the mainsite, and make sure you consult the Guides as necessary.
Naturally, standards have changed over the past couple of years, so it's a good idea to familiarize yourself with what kind of quality is expected now. If you'd like examples of what makes a successful SCP nowadays, consider taking a look at the list of top rated pages of this month, and the accompanying archives if you'd like to look back in time a bit.
If you're looking for some inspiration or advice on how to generate ideas, you can read the Essays on Style, where some writers of the site talk about their personal writing processes and idea development strategies.
Feel free to contact me or another staff member if you have any further questions. Welcome to the site!