[G1 Q&A, Help & Troubleshooting] Six6Sicks:
Follow these steps. I do them every single time before flashing a ROM, never have any issues that others have because they are lazy and refuse to just start fresh. I'm going to make this as basic as possible just to make it easy. It looks long, but I can seriously do this in under 3 minutes now.

You can either remove everything off your SD card and transfer on later, or leave it. It depends on if you want to resize your fat32 partition.

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If you don't have Amon_RA's recover get it Here

Boot into recovery (power on phone by pressing home button and power button)

Once in recovery, select (Go to console)

Press Enter

at the /# type this in

parted /dev/block/mmcblk0

Press Enter

When this pops up (parted), type in print

Press Enter

You should now see something like this:

Model: ([B][COLOR="Red"]whatever model your SD is[/COLOR][/B])
Disk /dev/block/mmcblk0: ([B][COLOR="Red"]the size of your SD card (write this # down for reference)[/COLOR][/B])
Sector Size (logical/physical): ([B][COLOR="Red"]Sector size[/COLOR][/B])
Partition Table: msdos

Number Start End Size Type File system Flags
1 512B 7405MB 7405MB primary fat32 lba
2 7405MB 7905MB 500MB primary ext2
3 7905MB 8001MB 96.0MB primary linux-swap(v1)

This gives you a break down of how much space is allocated for each partition.

The start/end/size values will differ depending on the size of your SD card and partitions.

Write down the size of your sd card, you can find it above next to:

Disk /dev/block/mmcblk0: ####MB

From here you can now delete and resize your partitions.

Number:

1 - fat32 partition (where you store music, photos, etc.)

2 - ext partition (where apps2sd goes)

3 - swap partition (used for swap)

Before you start deleting, make sure if you do want to remove the fat32 partition, you mount your SD and copy everything to your PC or wherever so you can transfer back later.

To remove individual partitions, type in at the (parted)

rm 1 Enter (this will delete your fat32 partition)

rm 2 Enter (this will delete your ext partition)

rm 3 Enter (this will delete your linux-swap partition)

Depending on what you deleted, you can type print Enter, again and it will refresh the partitions.

Using the number you wrote down which is the size of your SD card, you can figure out how you want to allocate the partitions.

I will show you what I type in and you can go off of that.

I have a 8GB SD card. 8169MB total

7405MB - fat32

500MB - ext2

96MB - swap

I only use 8001MB just to be safe. (not sure if it matters)

You just don't want to go over your SD card size.

Now to create the partitions.

The sizes below are my settings.

You can decide the sizes for you own SD card.

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For fat32 type in at the (parted):

mkpartfs primary fat32 0 7405 press Enter

This will create a 7405MB fat32 partition

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For ext2 type in at the (parted):

mkpartfs primary ext2 7405 7905 press Enter

This will create a 500MB ext2 partition

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For swap partition type in at the (parted):

mkpartfs primary linux-swap 7905 8001 press Enter

This will create a 96MB swap partition (you can upgrade to ext3 and ext 4 through the recovery)

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Notice the numbers I entered in 0 7405 (since 0-7405 = 7405, that's the size of the partition. Yes elementary, but just so you know what the numbers represent)

7405 7905 (7905-7405 = 500, 500MB partition, and so on)

You can choose whatever you want for the sizes of the partition doing it this way. Just make sure fat32 partition starts with 0, you want fat32 partition first, ext 2nd, and swap 3rd.

Once you have created the partitions, reboot into recovery and flash your rom.

To reboot into recovery, type quit at the (parted)

Then reboot recovery at the / #

It may look hard, but it is really simple.

Good luck.

All the credit for this goes to 51dusty and his thread Here

I just made this so you can do the same steps from your phone.