For what it's worth I'm an advocate of dollar cost averaging. Site sponsor Gold Stackers allows you to buy an ounce of silver and a gram of gold unallocated and you can build that up to whatever takes your fancy. Failing that put a bit of money aside and when you see a great deal on here or other site sponsors (eg Aurura et Luna) buzz that bargain.
How much to stack? Just keep stacking until you think to yourself "You know what? I think I have enough"
Hi AGR999 - if you haven't watched it yet, the fairly recent Mike Maloney video just posted on here http://forums.silverstackers.com/topic-25939-new-maloney-video.html gives a pretty compelling reason using the 200-day moving averages for both gold and silver as to why "now, without delay" is not a bad idea. (If you need some more confirmation bias for why we all say "buy buy buy" haha)
At a more micro level, the recent regular "Friday dip" seems to be very helpful too, and is one tactic you could use to dollar-average purchases (as many fine folks have already indicated here) while trying to buy low.