Miracle Gro will not only work, its an excellent product, so long as you use it correctly.
First of all, when your plants are small, don't use it at full-strength.
Next, don't use it every time you water. Once a week is plenty.
Alternatively, if you feel like you want to use it with every watering, then use it diluted to maybe 1/3 strength.
Once you switch to flowering, you'll see better results with the "bloom buster" flowering formula rather than the regular formula.
Lastly, listen to your plants (or more specifically, watch them closely!).
If you see the leaf tips turning brown, you're using too much fertilizer. . .back off.
If the plants are WAY dark green, you've got plenty of fertilizer. . .back off.
If you're going to use soluble fertilizer like this, make sure to flush your soil will pure water every few weeks to prevent salt buildup.
Depending on your strain and what type of soil, you may see some benefit adding a little extra magnesium over what's in the Miracle Grow. Diluted Epsom salts will work fine.
As to concentration, I'd start with the indoor formula. Remember, you can always add more fertilizer. . .if you add too much its possible to seriously stunt or even kill your plant, and that's very easy to do with something like Miracle Grow if you're not careful.
