Look at your challenge log first. That's free xp every week just doing different content,

Lower levels into the teens go pretty quick, just do quests in the starter zones, fates as you run passed, and city quests. The quests rewards can keep you at okay ilvls.

There's the Guildhest and Guildleves that you unlock at different outpost. Do enough of both of those to get your weekly challenge log rewards.

Also do your Hunt Log, it's different for each class and is worth keeping up on (it also serves as a good 'pointer' on where the next zone for fate grinding can be - so do leves).

So mostly: Check your challenge log, do all the things to get your weekly EXP rewards, do quests that are available at your level for updating gear, Fate grinding. At 30 you could start trying PvP - but that's not for everyone and is hardly necessary (or fast, the queue times aren't the greatest).