Cleaning It Up
Get an air compressor and blow out things like dust, spiders webs, leaves etc. You can blow out your engine bay doors and windows and boot with it.
Also use a paint brush to get rid of things the compressor doesn't get.
Now to do the taillights here's  before shots of them.
There's 8 screws each side to get of a taillight to get them off.
Once off use a heavy duty cleaner and an old toothbrush to get rid of any things like spiders, moss and grease. Also a compressor works well with blowing out the moss etc.
Once there done they should look like this except mine still have old rubbers on them you can take them of  if  you like but I left mine on for now until I buy some.
If you decide to paint them then you will have to leave them out to dry. a coat hanger does the job.
Now to take the lenses of  taillights there's also 8 screws each side.
They are numbered too the indicator is B15 and the middle one is S15 and the other one R15
To clean the lenses you a plastic cleaner called Plexus it works really well for cleaning up very dirty plastic.
When you've done that can screw them back in. Also screw in the black and silver front plate too.
Then they should look like this. Except mine aren't painted yet.
Now to remove the seats.
Here's what a seat from my car looks like.
To remove the front seats there's 4 13mm bolts some you can reach with a ratchet others you need a spanner.
Then just pull it out like so. Watch out though there pretty heavy.
Whilst we were pulling them out I noticed that a mount for the drivers side seat was broken. and there was a big huge hole where it was too.
This what my car looks like with no seats.
If your car has old crappy carpet like mine then chances are you want to get rid of it. remove the carpet by taking of the door scuff  which have plates and pulling the carpet out from under them.
Now for backseats a before shot of them.
There's only two Phillips head screws to get this puppy off.
Now the bottom part is going to come off.
For the top part  there's two clips that hold them in.
Then it will come out.
And this is what your left with.
Now to remove  the rest of that stinky carpet of yours. here's some before pics.