It really depends on the concentration of the product. If it doesn't list the kavalactone content per ml, it's probably a bullshit weak preparation. Most commonly available kava products are terrible. If the product doesn't list the kavalactone content (whether pills or tinctures), then I wouldn't even bother with it.
The effects vary substantially product to product as well. Very good quality products produce effects for me around 400-500mg of kavalactones and some others take 600-800mg. You should start lower though, I would say no higher than 200-300mg to see how you react first. The tinctures often contain about 1-2mg per drop if they are standardized but this can vary rather considerably so if the kavalactone content isn't specified, start low and titrate up.
As far as what you put it in, I would advise something with flavor. You can add the tincture to anything. I usually take about 2oz of juice or flavored water and add it in and take it like a shot. With a lot of drops in the juice, it will still taste bad but quickly as a shot and a chaser, it's tolerable.