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Both are almost full and I'm not finding it that easy to work out which files to delete
I use an App called File Manager which is pretty good. (looks like a white folder in a blue box if that helps)
The iPad you should be able to plug in to iTunes and it will tell you what is taking up the storage, alternatively use the check in the settings menu to see what App is using it up.
For the mac there are quite a few disk managers around that will show you the breakdown of files, you can use the search function to highlight large files on the disk. But I like Disk Inventory X for highlighting the things I can get rid of.
The biggest issue that I had on my MacBook was backup files from all my other apple devices.
Family with 3 phones and 2 iPads meant that I had over 40GB of back up files on my Mac!
I bought a cheap app for my Mac (forgot the name it cost £1.50) but all it did really was delete the downloads folder contents and clean up the trash so I never used it again. I would check your email, if you have lots of sent/received message with attachments they take up tons of space. A 1TB external disk is cheap, £50. Just buy one of those. It's not that hard to update the internal drive on most Macs, I upgraded my 2009 Mini from 160gb to 750gb (cost £60), so if you feel competant you can put in a newer faster larger hard drive or spend more and get superfast SSD.
As for the iPad if you link it up to iTunes on your Mac you'll get a more detailed breakdown of the contents. Again mail is a hog (attachments are included in "others"), try cutting down the mail history you keep on the iPad (you can always search online when you have WiFI). Also do you synch all your music / movies / photos - do you need to ?
You might want to have a search of the MacRumours website/forum too.
On the Mac, I use [url= http://www.omnigroup.com/more ]Omnidisksweeper[/url] - it is a simple app for finding space used. Costs nothing as well which is always nice.
Disk Inventory X fore Mac OS X. TreeMaps view. Lovely.
Shared code with WinDirStat for Windows..
Also check out Daisydisk