More descriptive and helpful, by King;
Level 1-15, cut Normal trees anywhere around the game, best option is to do cutting laps around the inside of the Grand Exchange.
Level 15-30, cut Oak trees right outside the walls of Varrock, on the East and West sides, and use the banks inside Varrock.
Level 30-45, cut Willow trees South of the bank in Draynor Village, and also right outside the walls of Lumbridge Castle on the East side.
Level 45-60, cut Maple trees right outside the Seer's Village bank in Camelot, and also all over the Northern area right outside Seer's Village.
Level 60-75, cut Yew trees right inside the North-Eastern walls of Varrock Castle, and also the Tree yard South of the Seer's Village bank.
Level 75-99, cut Magic trees scattered around the Gnome Stronghold and right outside the Gnome Stronghold in by the corner that has the Gnome Agility Training Arena.
I'm sure there is a lot more areas people use now, but these were the areas I mostly used during my training of 99 woodcut. Hope this helps! =)