How can I make a better world generation script? [closed]

local blockData = require(script.BlockData)

local maxWorldHeight = 25
local mapSizeInChunks = 8
local chunkSizeInBlocks = 5
local blockSize = 4

warn("Total Possible Blocks: "..((mapSizeInChunks*mapSizeInChunks)*(chunkSizeInBlocks*chunkSizeInBlocks)*maxWorldHeight))

function deriveBlockPos(chunkX, chunkZ, bY, bX, bZ)
    local nX, nY, nZ

    nX = bX*blockSize+(chunkX*(chunkSizeInBlocks*blockSize))
    nY = bY*blockSize
    nZ = bZ*blockSize+(chunkZ*(chunkSizeInBlocks*blockSize))

    --print(nX, nY, nZ)
    return Vector3.new(nX, nY, nZ)
end

for chunkX = -mapSizeInChunks/2, mapSizeInChunks/2-1, 1 do
    for chunkZ = -mapSizeInChunks/2, mapSizeInChunks/2-1, 1 do
        for bY = 0, maxWorldHeight do
            for bX = 0, chunkSizeInBlocks do
                for bZ = 0, chunkSizeInBlocks do
                    local newBlock
                    if bY == 0 then newBlock = blockData:GetBlockFromServer("Stone"):Clone() end
                    if bY ~= 0 then newBlock = blockData:GetBlockFromServer("Dirt"):Clone() end
                    if bY == maxWorldHeight then newBlock = blockData:GetBlockFromServer("Grass"):Clone() end
                    newBlock.Position = deriveBlockPos(chunkX, chunkZ, bY, bX, bZ)
                    newBlock.Parent = game.Workspace.WorldHolder
                end
            end
            wait()
        end
    end
end

I want to be able to generate mountains, rivers, caves, etc... How would I go about that, while also keeping it to a fairly quick rate? Right now it's 80-82 seconds to complete.