Is the format good or is there a better way to write it in this script?

Referring to your "elseif" format

In Lua, there is no switch statement like other programming languages, so the whole "elseif" thing is the best way to do it. While there are other ways like using tables to connect functions together, it might just make it more complicated:

local number=1
function switch(c)
  local swtbl = {
    casevar = c,
    caseof = function (self, code)
      local f
      if (self.casevar) then
        f = code[self.casevar] or code.default
      else
        f = code.missing or code.default
      end
      if f then
        if type(f)=="function" then
          return f(self.casevar,self)
        else
          error("case "..tostring(self.casevar).." not a function")
        end
      end
    end
  }
  return swtbl
end
local number = 1

function onMouseButton1Click()
    switch(number):caseof{
    [1] = function() return "It's 1" end,
    [2] = function() return "It is 2" end,
    [3] = function() return "dudeboy, it's 3" end
    }
    number = number + 1
end
script.Parent.MouseButton1Click:connect(onMouseButton1Click)