You can specify frame size and position at any time, including at Emacs startup and interactively, incrementally.

At Emacs Startup


Programmatically (e.g., in your init file)

    (add-hook 'after-init-hook '(lambda () (w32-send-sys-command #xf030)))
    (when window-system (set-frame-size (selected-frame) 80 24))
    (add-to-list 'default-frame-alist '(height . 24))
    (add-to-list 'default-frame-alist '(width . 80))

Both Interactively and Programmatically

These libraries let you resize frames either interactively or by program:

CategoryFrames CategoryDisplay FrameModes CategoryGlossary