Have you a wire brush? That's good for any little bits that don't shift, and for sweeping out the ovens.
If the inside of your lids are grubby then a couple of ice cubes on the plate then put the lid down should start to shift the dirt. Then you can use a brillo pad in circular motions to clean. It is very hot, so is use a pair of tongs to hold the pad.
When boiling your kettle, keep the spout turned towards the inner lid to keep it clean
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Invest in a little scraper - the type for ceramic hobs - use it to gently scrape any grease deposits you get round the edge of the plates on the enamel.
You need to be very careful with what you use on the enamel as it can be ruined by the wrong product.
I bought a paste for the enamel from the Aga cookshop website
You can get other stuff from a place called Blake and bull - they have videos to show you how to do stuff.
We inherited an aga in our house and love it now, but it just needs a bit of different looking after