I use it all the time with conditioner. I have super blonde and baby fine hair. It adds a little bit of body to the hair and adds a great shine. I keep bottles of it by the gallons around because I do use it all the time. I mix a little bit of lemon juice (1/4 cup) with a 2/3 bottle full of conditioner and massage it onto dry hair and let it sit for about 30 minutes. Rinse and then use it as a rinse just so conditioner isn't so heavy in my hair and let lemon rinse go for about 3 minutes. Then rinse. My hair comes out really shiny and beautiful.
Everyone's hair is different lemon juice gave my light brown hair some red tones. Oh and peroxide well I would skip that. Turned my hair bright orange. Awful, not cute at all. Took a professional trip to the salon to fix.
My sister used to put it in her light blonde hair every summer, then layed out in the sun for an hour or so, to give it lighter highlights - and it did work. Looked nice. But it lightens it to the base - a neighbor had dark blonde hair, put it in and it turned it a reddish brassy color. Looked horrible. But after a few hours, give it a deep conditioning. It'll dry your hair out horribly.
Don't try peroxide - every single person I know who has tried that had their hair turn a horrible orange-ish color.
A few years later something called "Sun In" came out that worked much better and faster and didn't dry out her hair, so she started using that and the lemons went back to being used for lemonaide.