Remember that the law in England and Wlaes is such that you can legally back out of any deal that has been made up to the exchange date (or indeed renegotiate the deal up to that time), as opposed to Scotland where of course once you've agreed a price it is binding.
So how do you stop yourself getting gazumped? Well one of the simplest things is to request that the sellers remove the property from the market immediately: go through the estate agent to request this. Of course this won't guarantee it happening, but often that is enough to get the property taken off the market and therefore minimise the chances of being gazumped as it won't continue to be listed.
Whether the seller does this will depend on a few factors, not least of coruse whether they are genuinely happy with your offer and whether you have offered their asking price or not.
In terms of the sale process itself, then people have all sorts of stories about dealing with solicitors and how hard it can be - therefore if at all possible get a personal recommendation as to a good solicitor that you can use that is fast and reliable and doesn't need to be chased all the time to do things.
With regard to getting your own house in order, as it were, with regard to your finances and all that you need to be happy to set a completion and exchange date, be sure that you take your time so that everything really is in order. If there is pressure coming on you to agree an earlier exchange and completion date then you would like, don't be at all scared to keep firm and set it at a time you know you can meet and are comfortable with: after all, if you fail to have everything in place and can't complete when agreed, it is possible that you might have to pay the seller's costs.
Ultimately, the hope is that you get through completion and exchange of contracts smoothly, and then you can enjoy receiving that call from the estate agent or solicitor letting you know that the property is yours (oh - and request that you pay their solicitor's bill and stamp duty, if you need to pay it).
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