Port a Rom the Basic way [no signing - no compiling - no special software]

Use a CM Rom for your Base as these are tried and tested (you can use Stock also as long as you are porting to another similar Stock Rom hardware)
(Make a backup copy of all the files your download - you may need to extract the files again later)

Find your a working Base Rom for your mobile and extract the contents to your desktop, then delete the following folders from the desktop
system/app
system/fonts
system/framework
system/media
system/priv-app

Edit the build.prop file in the Base Rom >system folder to reflect your new Port Rom details - these vary depending on the port your are using
The lines you need to look for are as follows;
ro.build.id=
ro.build.display.id=
ro.build.date=
ro.modversion=

Now find the Port Rom you want to go to making sure it is close to your manufacture as possible [for example; xperia SP use xperia Z - these have similar screen sizes and hardware]
Extract the contents as before and now copy the following folders back into the Base Rom on your desktop
system/app
system/fonts
system/framework
system/media
system/priv-app

Now open the original Base Rom .zip (do not extract it) with winzip7 or winRAR and delete the following folders
system/app
system/fonts
system/framework
system/media
system/priv-app
Now with the .zip still open 'drag and drop' ALL the folders from your desktop Base Rom into the now open base Rom .zip over-writting any existing files/folders
Do not save just close the .zip and upload to your mobile sdcard, enter recovery, flash and enjoy.

Possible Issues and solutions:
You may need to remove the kernel in the Base Rom and sideload one more appropriate to your new Port Rom - flashtool is good for this
Recovery Crashes - error codes 6 or 7 are mainly caused by corrupted zips, bad partitions or poor coding in the updater-script file
Boot issues and strange video issues are mainly a cause of framework incompatibilities - try another Port Rom closer to your mobile hardware

I use this method for all my ports - the hardest part is finding a Base Rom, the next is realising the Port Rom can take hours of trials and errors
I never bother editing the framework files I just move onto finding another Port Rom closer to my Mobile Hardware
The least you mess about with the least there is to go wrong!!!

If you are very confident and can work with open .zip files on the fly you can perform all the above without the need to extract much other than the build.prop
Simply with the 'drag and drop' method between the two open .zip files

This possibly won't work for Miui as that requires a little more editing and work
Hope this helps someone