For my compost bin i do 75% green/nitrogen - 25 % brown/carbon, its just a guide line really i add other stuff like bananas for potassium - kitchen waste etc. If it stating to get smelly you got to much Green, it wants to be smell earthy . Keep it well aerated by turning it, or into one compost bin into the other easiest way. Dont let it get to wet it will slow the process down, i use a carpet for the top
I nearly fill one of my compost bins about 3/4 weeks ago with loads of bedding plants, i put them right at the bottom of the bin when i was turning it. i thought it would take ages to break down, turned the compost bin yesterday and it all broke down already which surprised me a bit. I spent £40-50 last year on compost so i can make a nice saving next season hopefully unless i go mad and want to grow more plant
No perennial weeds / weeds with seeds on. Annual weeds a fine as long they not seeding
Might be best to put leaves in a separate pile its up to you. they can take a while to break down. Monty puts leaves in a bin bag - fills with water - makes holes in the bottom then put them to the side for a year. I suppose it depends on the quantity of leaves you are adding what will determine how fast they will compost.
Be careful you don't put to much grass cutting in, it can get quite compact and stops air flow and can dominate a bin and smell.