I started with this…
http://www.wolfensteinx.com/surface/tutorials/et_getting_started.html
and all other Tuts there are very usefull too…
Next… read this topic here
http://www.splashdamage.com/index.php?name=pnPHPbb2&file=viewtopic&t=1710
If any other needs try to search this forum http://www.splashdamage.com/index.php?name=pnPHPbb2&file=search
Need any more help post a Need_Help explaiuning what problem in mapping you particullary have… Nobody can help you mapping if you dont start mapping your self…
Tips:
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Start with an idea of what the map will be.
a) What texture scheme (rocky-grass, grass, desert, town, snow… etc.)
b) where will it be takeing place… (what will be the detailed objects there - restaurant has tables, chairs, a bar “maybe”)
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Draw a sketch of your map.
this will be usefull when you map… you can schedule what you want to do first, second… and see how the particular things you drew on your sketch looklike in game.
(you can always make changes)
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Start with either of these places…
a) Obective
b) Attackers Spawn
This will help you keep straight on the point of what you do… Unless the map will be just a fragging map - TE_VALHALA for exemple.
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Map… Map… and map…
I did a lot of usefull stuff befor I started on the project I am atm…
The stuff I made befor came usefull now… as Prefabs 
Get a free hosting for your pictures and other stuff in case you want to show ppl your progress… problems… or other stuff ppl might download.