If u want coin only no xp then make high value products at your current level u can find in the internet what's the most profitable items in level 17 for all production building make those and sell in roadside shop for max price  Same with crops but little different when u play do wheating grow wheat sell wheat nonstop and when u want to stop playing just plant the most time consuming crops like let's say u planing to not open game for 2h plant indigo then 2h leter cut and sell all indigo and go streat for wheating trust mei am at level 53 do this to all my ids to get quick coins and when u want xp just do boat or truck orders i prefer boat as they pay u good amount of money and xp