Definitive Android SDCard folder structure

In the root of the external storage (SDCard) save your shared files in one of the following directories:

Music - Media scanner classifies all media found here as user music.
Podcasts - Media scanner classifies all media found here as a podcast.
Ringtones - Media scanner classifies all media found here as a ringtone.
Alarms - Media scanner classifies all media found here as an alarm sound.
Notifications - Media scanner classifies all media found here as a notification sound.
Pictures - All photos (excluding those taken with the camera).
Movies - All movies (excluding those taken with the camcorder).
Download - Miscellaneous downloads.

from : http://developer.android.com/guide/topics/data/data-storage.html#filesExternal

ClockworkMod Recovery Custom ROM procedure

Everytime I install a new Rom, I double check to make sure it has a boot.img, then upon using CWM to install it, I first do the following(some of them are redundant, but I do so for good measure):

• wipe data/factory reset
• wipe cache partition
• advanced > Wipe Dalvik Cache
• advanced > Wipe Battery Stats
• mounts and storage > unmount cache
• mounts and storage > format /boot (If the rom had a boot.img)
• mounts and storage > format /cache
• mounts and storage > format /data
• mounts and storage > format /system

Then I install the ROM zip, and if I want GAPPS, I flash those afterward.
Then reboot.

This ensures that ALL data is gone, and it will not allow for unique bugs caused by remaining data from a previous rom.

from: http://forum.xda-developers.com/showpost.php?p=32947067&postcount=11

Cyanogenmod Partitioning SD Card

Partition the SD card
- Scroll down, and select “Advanced”
- Select “Partition SD Card
- Choose your Ext Size (I recommend choosing half of the storage space that your card is.
   - For a 256mb card, select 128M
   - For a 512mb card, select 256M
   - For a 1gb card, select 512M
   - For a 2gb card, select 1024M
   - For a 4gb card, select 2048M
   - For a 8gb card, select 4096M
- any memory card higher than this will not be partitioned, the phone will not be able to read it properly, but I would recommend an 8gb card, and if you have any smaller than 1gb, I wouldn’t even bother wasting your time – but go ahead if you wish.
- Now it will ask you what Swap size you want:
   - If you have a 256mb or a 512mb card, select 0M.
   - If you have a 1gb or a 2gb card, select 32M.
   - If you have a 4gb or a 8gb card, select 64M.
- If it asks to confirm, select yes, now wait for a few minutes, and reboot