For us personal spending is anything we spend on ourselves - clothes, hair, beauty, social, gym or exercise classes, contact lenses/glasses (we both wear them), books, magazines, music, gifts for each other. If we eat out together we will generally pay for it from our personal accounts unless we have enough in the joint to 'treat' ourselves.
We do occasionally put personal stuff through the joint account. DH wears suits for work whereas I work from home so wear casual. So when he needs a new suit we usually put that on the joint account as it's a much bigger expense than I would ever incur (but equally if I ever go back to being an employee rather than self-employed and need a suit for interviews then the joint would probably pay it)
I spend more on hair as he barely has any, but he spends more on clothes as he prefers pricier jeans to me! I think if only one of us wore glasses we'd probably put those on the joint account as that would be a big lopsided expense. We try to keep it roughly fair but allow each other the freedom to spend without having to discuss everything or sign it off. Recently we realised that DH was actually buying lunch every day with his money but I get to dip into the fridge which is paid for out of the joint account, so we allocated slightly more to his personal expenditure to account for that.
It has worked well for us for 11 years now - when we first moved in we kept more for ourselves (but always an equal amount each despite me earning a lot more at the time - now he earns a lot more but we still keep the same amount) but would often have to pool money for certain things and the joint account was mainly for rent and utilities, but as we got married, had kids and I had mat leave, went self-employed etc, it made more sense for the joint to be the main account for all sorts of bills and the personal to be really personal stuff only. So you could start small with just having a joint account for the key household bills and then settle at a situation you are both comfortable with.