Building a Team
When you have come up with your basic idea and sketches, work on putting together a nice clean outline. Start by outlining your game in the simplest format, listing genre and basic ideas. Then, make short and medium length paragraphs describing your game in detail. Here's an example:
This is essentially a quick synopsis to introduce the game. If there is any concept work, prepare small thumbnails of that as well, in addition to any information regarding technology tests you have completed. Now is the time to figure out how many people you need. For a game like this, I'll really only need total a programmer, an artist, and a musician, although I could use existing music loops, or, in my case, my own music and art. I can always ask some friends to test it when I get far enough!
When it's all ready, it's time to find people!
Where
So you have your synopsis, a good idea is to check out the Site List thread on the forum for graphic artists, as well as occasional threads in the Help Wanted forum.
If you would rather, you can also post a thread in the aforementioned Help Wanted forum with the synopsis of your game, who you are looking for, and information on what styles you need. Be sure to outline the art style, time the project will be under development for (estimation), if it is commercial or not (note that you must have purchased the personal edition of Construct to create a commercial game), and any info on the musical or general game mood if you need a composer. The devil is in the details, and the more you give, the easier time you will have finding what you are looking for, especially if you give a good looking presentation! This method generally takes a longer time than going and directly finding people, so I only suggest it if you have time.
If you still have no luck, you are welcome to look outside the community. Places such as the Newgrounds Collabinator and forums are great places to look, as well as across DeviantArt and the internet in general.
Who
Now you need to figure out who you REALLY want on your team. Look for people who have:
1. Completed games in the past
2. Are skilled at what you need them to do
3. Appear to be friendly and good to work with
4. Show genuine interest in your game (not just a standard response that looks like they copy and pasted it to you)
Check out their art/music and play through any games they have made or participated in... see if it's on par with the quality AND style you are looking for. Ask them about any long term projects or possible conflicts with development. If you have money or are planning to sell the game (once again, you MUST have the personal edition or business edition to do that), you can also work out payment with people for their work. Payment generally guarantees that the work will get done, while projects done just on love alone often falter.
Note that you do not need testers or composer(s) to begin. They are elements that are added later when development is well under way, except in certain cases, such as a music-driven game or a very fast development where new features are commonplace and a steady testing group is needed from day one.
At the end of the day, it is your judgement and ultimate responsibility as project manager to pick the people you feel are best for the development! Just remember that a really good pixel artist is worthless if your style is vector animation and they don't have any experience or tools to do that, same with a brilliant programmer who uses Java and has no interest in Construct's interface or a composer who writes sick dubstep beats and you need orchestral. Yes, people often can learn other skills, but it's best to find people who are fluent in what you need, because not only can they do it faster and better, but they just plain know what they are doing. Do not just find people who sound interested and have no clue what they are doing either, that is a recipe for disaster.
Assembly and Coordiation
When you have figured out who you want on your team, you have several options on how to bring that team together. While the exact technologies will be discussed later in the next section, I will go over the basics of activity and how to get everyone together here.
Your primary concern developing a game is and always will be networking, which is keeping steady communication between all members of the team in order to produce progress. If you have to wait days to communicate with people for short amounts of time, there's no point in having them on the team to be honest. I would take an active intermediate artist over an inactive professional artist any day, because the amount of information that can go back and forth and slow, steady polishing that can occur is incredible. Staying up to speed is a challenging task, especially when some of your team might be from the other side of the world!
As project manager, you will need to explore basic features and "pipelines" to get things done. For instance, you will need to figure out how a character gets designed. Do you sketch out some ideas, then work with one artist to create the actual product? How about the tasks of each member... let's say you have two artists. Should one do the tile sets and menus and the other do the props and characters? These decisions need to be made, and by consulting your team members, you can figure it out as you start production. Generally, it's best to have a good plan before diving in, but always remember to consult your team members first!
Sidenote: Contracts
If you are developing a game involving a lot of financial assets or high-caliber members, it is wise, if not necessary, to create and abide by contracts drafted up to protect the game and the development. NDAs (Non-Disclosure Agreements) protect the game information from being "leaked" without your permission before release, and also offer peace of mind. While most small game developments don't require contracts, they are an important part of the "larger business" and you will probably run into one at some point. If you choose to use one, it is best to find a legal adviser or that brother of your sister's friend who studied law and ask them to draft it up, or, if you are the receiver of one, decipher its cryptic passages.