So here's my own personal "lesson's learned" that hopefully will help you if you find yourself doing contract work:

Ok, so this is the first step. Assuming you were given sufficient information about what they want, then you should really think about what you're capable of doing and whether or not you should take this job. Personally, my rule is, if I know it's possible, I'll say yes, even if I don't yet know how to do it. That's because the internet is such a great help, it would be rare to run into an issue that you can't figure out with some help. So if your clients are asking for something that you don't yet know how to program, but you know you can do it on the platform then go for it. How else are you going to learn?

Use this rule with some limitation, however. If you're really lacking the expertise or foundation in something, then unless you have tons of time to complete the project, then I wouldn't say yes. For example, I haven't personally done any 3d/openGL programming yet so I wouldn't say yes to a project that extensively uses it.

This part can be tricky. There is no set formula really, but I have some tips for pricing that will hopefully give you a better idea on how to confidently ask your price and have them accept. Here are some personal guidelines

So now that you have the price, you want to make sure it feels justified to your client. I never set a price before I can really think about everything. For example, if you're still in your introduction phase, and they want a price, don't give one! Just comment that you will send them a proposal sheet with all the features outlined, and a price for everything. You don't want to shout out a low number and then deliver something that is way higher. You also don't want to shock them with a big number before they feel like they are getting a great product.

Make up a proposal document in a word editor. Personally, I leave the price till the very end. Why? Because by the time they reach the end, you've already discussed all the great features you plan to implement, and how it's the best product they'll ever use, etc etc...so your price comes off as a steal! If you hit them up front with a price, they will read through the document with a negative bias. Think about those commercials on TV. They always go on about their product, then at the end, ask "What would you pay for something like this? $100? $50? How about $20!!". This is not by accident.

You have two options then. You can either polish the hell out of the application, and even throw in a few bonus features (assuming they are in-line with the customer's needs) or you can sit and wait on it until you near your deadline.

Why don't you want to turn it in too early? Because you should treat that extra time as a surplus. If you said it is going to take you 3 weeks, and it took you only 1, you have a surplus of 2 weeks. I personally don't want to let them know that I can do a 3 week project in 1 week. Why not? Because that may not always be the case! I may later have a 3 week project that takes all 3 weeks, but if I set a precedent of delivering super early, then the pressure is on for that longer project. It also makes it harder to quote longer times if you keep delivering too early.

Feel free to deliver early, but again, don't do it too early. They may also wonder why they paid you for 3 weeks of work if you're done in 1. They may further wonder if the product sucks, or what is wrong with it, if it's done so early, etc.

I would just polish the application. Everyone loves polish in their applications. The smallest details are what make an application go from "functional" to "fantastic". And since you are still delivering on time, then they are still going to be very happy with you.

So this is not a fun scenario to be in, but it'll happen. Sometimes the scope of the project gets out of hand. The best policy here is OPENNESS/HONESTY. Tell them that the project is taking longer than expected, and give a reasonable time for when you think you'll have it done. I typically explain it in a way that makes it sound like it isn't something that I did wrong, but it's just something about the nature of the project.

This really goes for any scenario, to be honest. Just continue to stay open and communicative about your progress. This doesn't mean that you should email them every five minutes (unless they want you to), but it does mean that maybe every few days or once a week, give them an update on where you're at, and what's next. They'll be happy to know they are paying for progress, and it'll make it easier to ask for an extension when something goes wrong, because they know that you've been working on it all along.

In general, contract work is really fun and rewarding. It's nice to learn new things all the time, as mandated by the project ,and to challenge yourself to do things you may not have done before. The key is to build a great relationship with your clients for future work, and for recommendations. I am always very honest with them and I never promise something I can't deliver. Again, under promise, over deliver!

I hope this has proved helpful!

Cheers,
samerpaul