Lavender ??

Also how do I make sure I get all the blonde bits ? Do I slap some on the freshly dyed brown bits aswell to blend in?

If it is directions Lavender, it is not a very strongly pigmented dye, so i wouldn't dilute with conditioner. You can thin it with a little water if you don't like the consistency.
If you do it in small sections and really squidge it in you shouldn't miss any. Lavender won't show on brown so don't worry about overlapping.
I usually wrap in a bag or cling film, foil would also work. it keeps the heat in (which helps the colour to absorb)and stops the dye getting everywhere

Thanks for reply how long should I leave on for

If you want maximum longevity then I would leave it on for at least 4 hours

Ok so I take it it would be fine to leave in over night ? Thanks again xx