It's quite difficult, particularly in the current economic climate, especially if you don't have a great knowledge or experience of the property market or building trades.
I think people now have generally 'missed the boat' in terms of being able to snap up cheap properties and sell them on for huge profits like they have been able to do in the late 90s/early 00s. Largely because there are fewer cheap properties on the market as they are all snapped up by developers and development companies who know what they're looking for at auctions and can tend to turn over properties quite quickly. It also helps to have quite a bit of capital behind you, so that it doesn't matter if the property you renovate doesn't sell immediately you're not faced with a mortgage you can't pay. The rental market is probably a safer bet for properties at the minute as it's a bit more steady than the sales market, but the return on your investment is slower and with an unsteady housing market, you might not even get much of a return on your money. Quite a few landlords are having to raise their rents at the minute to meet their rising mortgage, and for those tied in to 12 month fixed lease, it's difficult and some are having to top-up the rent to cover the mortgage if their mortgage payments have recently gone up.
You'd also need to be a good investment in the eyes of mortgage lenders as it's becoming increasingly difficult with this whole credit crunch thing. If you wanted to rent the property out once you'd renovated it, you'd need to look in to a buy to let mortgage which is different to a regular mortgage.
It is still possible to make money from property development in the current climate, but you need to be quite savvy and really know what you're doing. I wouldn't say it's the best time for an amateur to be trying things out, as the market just isn't steady enough and people are reluctant to buy, and unless you can easily afford to keep up mortgage payments on an empty property for possibly a year or more, it could pose quite big financial risks.
Personally, I'd be keeping an eye on property auctions. If you're looking to renovate a flat somewhere more urban then you're most likely to want to attract young proffessionals, so look in areas which are up-and-coming, look at the property prices for the area (you can find these on the net) and somewhere with transport links within a reasonable distance for example. It's probably best to start with something small and try and work your way up to bigger properties the more experience you get under your belt.
Also, build a portfolio of contacts within property and the building trade if you possibly can. Often people underestimate how much work they are realistically able to take on themselves and this can lead to budgets and deadlines being exceeded. If you know friends or families with reputable tradesman skills, ask their advice and get an idea of whether they'd be willing to help, and at what cost. I think time is of the essence really, if you look at the most successful developers, they have a very quick turnover time from when they buy the property, keep renovations within a few months max and have it back on the market. You have to have a firm budget and really really work to this, as it eats in to profits otherwise and profit margins today aren't as wide as they were a few years ago when the market was still starting to boom. Also bear in mind that anything structural may require planning permission - loft conversions, extensions etc, and these can often take a long time. If a property you view is listed as having planning permission (or having it pending), ask questions and find out how long it's taken, what it's for and what limitations there are.
Personally I would hold off for a bit until the market becomes more stable, unless you can risk having money tied up in a property that you can't sell or get any profit from renting. Ask a couple of estate agents for valuations of the property before and after renovations, for both sales and lettings. Get good mortgage advice and make sure you stay in control of your finances and keep to budgets as much as you can. Go for cheap but good quality and keep properties as a 'blank canvas' as much as you can - don't be tempted to decorate to your own tastes. Neutral walls and carpets or wood flooring are much more attractive to buyers than something that is seen as trendy now, or by you. A clean white bathroom and a well laid out kitchen, and some bright accessories show people that they could move straight in to the property and keep costs minimal. Make sure the property is marketed well too. Money can still be made, and the cheaper properties on the market now are still being snapped up by investors and developers, but as a first-time buyer or developer, I would tread very carefully for the time being.
(Edit: Sorry that got a bit long! Work in an estate agency so it's rubbed off on me!)