Recently I've seen a lot of people asking how to complete meta-events and other open-world PvE stuff which cannot be done solo. It seems that when content is popular lots of players rely on just being there at the same time as an organised group, and then when there's less people organising it they're stuck, but it's actually relatively simple to get a group together and anyone can do it, it just takes a bit of planning.
Steps 2, 3 and 4 should be done at the same time, I've just numbered them for clarity.
1) Find a convenient time to do it.
Ideally this needs to be when lots of people are online, during each region's 'prime time'. For EU that's roughly 16:00 UTC - 22:00 UTC (population doesn't really drop off until closer to 23:00, but relatively few people are willing to start a big event that late). For NA it's roughly 2 hours each side of reset - 22:00 UTC - 02:00 UTC, or about 4pm - 8pm Central Standard Time. (NA players please correct me if I'm wrong.)
Of course it also needs to be when you're online and will have enough time to form a group and complete the event, which could be an hour or two depending on what it is. If that's going to be difficult try to plan it for a weekend when there's a wider range of times with lots of people online.
If it's a world boss, meta event or something else on a timer you'll also need to check when it will be available. You can use the wiki to do that. This page lists a lot of timers: https://wiki.guildwars2.com/wiki/Event_timers but individual event, boss etc. pages also show their timers. You might need to plan ahead a bit to find a day when all 3 of these fit together.
2) Arrive early & advertise it in map chat.
Aim to get to the map at least 10 minutes before the event starts, ideally 15-20 minutes before. If there's any pre-events try to arrive 10-20 minutes before they start, and make sure you join in to help them succeed. Arriving early has 2 benefits - it means if other people are arriving for the event you're more likely to be in their copy of the map than a new one created as an 'overflow', and it gives you time to attract more people before the event starts.
As soon as you arrive ask in map chat if anyone is going to do the event, and tell them you're going to do it. Periodically repeat this so anyone who joined the map after you will see it and knows to stick around if they want to join in.
3) Use the Looking For Group tool to attract more people.
Unlike in a lot of MMOs this can be used for any content, including open-world events. Also unlike a lot of MMOs it's not automated - it's not a queue you join to be dumped into a group when there's space, it's more like an in-game notice board to advertise what's going on, which means if you don't see the event you want to do listed that doesn't mean no one is interested - just that no one else has taken the initiative to start a group yet.
All you need to do is find the right section for your event or activity, click the 'Advertise Your Group' button at the bottom and type a short message to let people know what you're doing. For example for Serpent's Ire you'd go to Path of Fire > Domain of Vabbi, click advertise and write something like "Serpent's Ire starting xx:30 - need commander". If it's needed for an achievement or collection it's a good idea to say that, because it gives players an extra incentive to join in. (Either because they need it themselves or because they want to help others get it.)
This is literally just letting players know a group is forming. You're not committing to lead the group or promising it will succeed or anything like that, and it can be done by anyone - you don't need a commander tag or anything to start a group.
4) Ask your guild/s for help.
Ask in guild chat if anyone can help you with the event and let them know when and where it is. Again make sure you tell them if you need it for an achievement or something because then they're more likely to help.
Ask even if it's not a dedicated PvE guild or this isn't the sort of activity you'd normally do together. You're not trying to set up a new guild activity, you're just asking the people you play with and/or chat to regularly to help you with something you're struggling to do alone. Even if it's a dedicated PvP or WvW guild you're probably not the only person who also plays PvE content sometimes and it's likely someone will be willing to come and help you out. (Just don't ask during guild activities - if your PvP guild has just gotten into teams and queued up they're not going to come and help you do an event.)
Of course if your guild does regularly organise meta-events you could ask the leader in advance if they can include the one you need help with.
Bonus tip for bounties: The timer on a bounty doesn't start until a player who has picked the contract up from a bounty board gets close to the bounty marker. That means you can form a group first then trigger the bounty when you've got enough people. This makes it much, much easier to complete because it means the whole group gets the full time to attack the target. (It also means you can gather at a waypoint and all go to the location together, instead of trying to direct people out to the remote locations some of them happen.)
Finally if you've got social anxiety, aren't confident you can write any of the games supported languages well enough to advertise or otherwise can't stand the idea of all that typing to ask poeple to help try finding 1 person to help you and then ask them to do the advertising.
Danielle Aurorel, Desolation EU. Mini Collector
"You can run like a river, Till you end up in the sea
And you run till night is black, And keep on going in your dreams
And you know all the long while, It's the journey that you seek
It's the miles of moving forward, With the wind beneath your wings"