Dyno-Gro (now rebranded Superthrive), Foliage Pro is the best seller in their range. It's a liquid plant food that's a bit different. Super-concentrated too. Here are the directions for use below.
Like most plant foods, directions for use change based on how you want to use it and how often you feed. Keep in mind when any plant food gives you a range, go for the higher dose when your plant's actively growing, or is a fast grower, and the lower dose for maintenance, in winter, or for slow growers. If you feed twice as often, don't double the dose! Keep the dose the same instead and double the water.
Here are the different doses for different uses below...
Every time you water (general maintenance): 1 ml per 1.5 litres*
This is the general maintenance dose. Also the same dose if you want to foliar feed, although for best results it's best to add Foliage Pro to water and feed via the roots. Officially the general maintenance dose is 3 to 7 mls per 10 litres, which is 0.3 to 0.7 ml per litre - but that does my head in (and my pipette measures in half ml increments), so to make it simple, I just feed 1ml Foliage Pro per 1 to 1.5 litres water every time I water.
Like all fertilisers, the occasional 'flush water' just with plain water and no fertiliser is recommended to help flush out any excess mineral salts that can build up over time (although build-up of unused mineral salts is far less of a concern with Foliage Pro).
If you have a quick check of the plant forums, you'll find most collectors have found their own ideal dose, but overall general consensus for indoor plants feeding Foliage-Pro is from 1ml per 1 litre water to 1 ml per 1.5 litres water.
Monthly watering: 2 to 4 ml per litre
If you find it simpler to feed less often, use the monthly rate instead. That's 20ml to 40ml per 10 litres, so 2 to 4 ml per 1 litre water. For active growers go for the 4ml dose per litre, and for slower growers or in colder seasons go for to the 2ml dose per litre.
I recommend feeding every time you water in order to avoid deficiencies in immobile nutrients like calcium. Once immobile nutrient deficiencies occur - that's it - you've got yourself a deficiency for life that your plant can't remedy later in the affected leaf / root / flower / fruit. If you feed more frequently than monthly, use the General Maintenance dose above instead.
Hydro and Leca: 1ml per 1.5litres
If you have a recirculating hydroponics system, go for 5 to 10 ml per 4 litres. But for non-recirculating systems like hydro in still water, and for leca, use the same level as general maintenance, above: 1ml per 1 to 1.5 litres water.
Note it's recommended to change the water weekly for non-recirculating hydro and leca to keep the water chemistry and nutrients balanced. If you're doing twice weekly water changes, keep the dose the same but double the water, so that's 1 ml per 3 litres.
Foliar feeding (misting & spraying): 1 ml per litre
Foliage Pro is suitable for foliar feeding (a fancy name for watering fertiliser on to leaves instead of into soil). Mix 1/2 to 1ml per litre of Foliage-Pro in your spray bottle or mister (choose the dose to match the plant's needs), and water all leaves until they drip. Foliar feeding in the morning is best so it dries on the leaf surface during the day.
Foliar feeding is only recommended in the short-term. Leaves absorb nutrients faster than roots, but can't absorb all the nutrients a plant needs, and also doesn't shift them as well to where they need to be. If there's a temporary deficiency you want to correct as fast as possible or the roots are compromised, foliar or leaf feeding definitely has its place for rapid relief. If a plant's under stress or on the decline, I've seen a sickie perk up well pretty fast following a foliar feed.