Get a list over playermade scenarios in OpenTTD:
http://wiki.openttd.org/List_of_player-made_scenarios

Read more about the requested features in OpenTTD here:
http://wiki.openttd.org/Requested_features

Try not to make parallel tracks too close, unless they are doing the same job. If you use two different tracks that are so close that the horizontal and vertical track sections share the same square, make sure you realise the consequences. When it comes to upgrading to monorail or maglev tracks, you’ll have to upgrade both tracks at the same time or reroute one of them so that they don’t share the same square.

I found this tip below in italic text on how to build in an area in OpenTTD on the net. But, I don’t use it when I play. I just carry on and build fast as possible to get things up and going.

Try not to upset the locals. Lots of building work in an area can make the local authorities mad with you. This can affect what you can do in nearby towns. Try to compensate by making changes over time, limiting the amount of damage you do, planting them some nice trees to hide the building work or even, in extreme cases, bribing the town in question!