Gnutella Network is not a central server based p2p 'system'...
It is a 'community' of individual sharers...
You CAN try to choose your Downloads to be first started from so-called 'hi-speed/broad bandwidth' fellow users, but that does not mean that you will go any 'faster' as, no matter how great a capacity bandwidth someone may have, if they are using it to the 'max' for a large number of connections it is not going to be particularly 'fast' for any one connection...
Try to download files which show the greatest number of 'sources'...
When you do this you have a high probability that you will be downloading the same file from more than one source...
You may be able to download one file from 10 different people at the same time...
This makes the transfer(s) much faster... Well, as fast as the bandwidth
you are allowing for downloads
This getting of files from more than one person at the same time is called 'swarming'... (Among other things...)
There are other 'tricks', but they all more or less involve simple experience in sharing on the network...
The longer you do this the more you'll notice about how to 'read' others and 'drive' the p2p client you are using...