any quests can be finished more quickly and safely with the help of a good group. Groups allow you to go places that you would otherwise not be able to go (and survive) by yourself.

Dungeon Finder
You can use the Dungeon Finder to find other players to party with. You can look for a group for yourself or look for additional group members.

Ask For Groups in Popular Areas
Sometimes it's good to start asking for a group in areas where players hang out. Main cities such as Stormwind are a good place to ask.

Guilds
Guilds are a great source of help. You should consider joining a guild because you might have an easier time getting help and finding groups. This of course depends on the quality of the guild you join. If it doesn't work out, leave the guild and find another one!

Meet Up On Site
Sometimes after traveling to a quest location you might find players already there. Ask them if they want to team up. For collection quests (collect x skins) people might not want to team, but for other quests, people will often like help. Give it a try. If you have two parties, see if you can merge the parties into one group!