Get your levels measured and dose accordingly. Most people are deficient in a number of areas, and you can get screened for them all at once.
In the absence of that, if you're just making a qualified guess, you should probably dose significantly more than 1,000-2,000 IUs/day. The daily intake required for toxicity to be an issue are very high (sustained total intake of around 20,000 IUs/day). It's also generally recommended that D3 supplements are taken alongside a K2 supplement.
Talk to your doctor. They can take a blood test and send it off to analysis. It can be somewhat expensive. When I said "all at once" I didn't mean that a simple biochemical test can reveal all deficiencies, obviously, but that a single blood test can be sent off to have many different tests done. I'm not yet sure exactly how it works in the US, sorry.
The kind of deficiencies I had in mind would be vitamin (e.g. D, K), mineral (e.g. iron, calcium) and electolytic (e.g. magnesium, potassium).
In the absence of that, if you're just making a qualified guess, you should probably dose significantly more than 1,000-2,000 IUs/day. The daily intake required for toxicity to be an issue are very high (sustained total intake of around 20,000 IUs/day). It's also generally recommended that D3 supplements are taken alongside a K2 supplement.