These edits are differcult to get right. Three things could do if you have not done them already are.
1. Read the Beginners guide in the wiki
2. Watch the videos
http://help.openstreetmap.org/questions/7170/videos-for-new-contributors
3. Then after the first two have been read and watched then using either Potlach2 or JOSM inspect a similar road network or junction to see what others have done, make notes. You can try things out some editing until you are sure you know how it works. but do not save it if it is incorrect. JOSM may be the best in this situation as you could have the data on your PC to play around with for some time so that you could leave the data on your PC for learning, when closing JOSM DO Not SAVE until you know what you are doing. Good Luck It may help to print out the map of the area or an aerial image for you to pencil in junction with lanes,one ways and note other stuff, you could use a camera as well. It will be much easier to do this edit with all the information as notes and sketches when you do it.