Plants that don't yield very well need some extra help during the veg period to promote better growth, such techniques as LST (low stress training), super-cropping, and topping and fimming.
I am going to focus on LST as this is my favourite along with super-cropping, mainly because this is what gives best results, with topping and fimming you are actually setting yourself back in the first week or two as it recovers so it requires a longer veg period, with LST and super-cropping you get the immediate result of redirecting the plants growth hormones (auxins) any points left above the bend or crop, basically you want to make your super-crop/pinch below the point you want to grow e.g the main stem at a point below the top branches, and this will mean the auxins are directed to the uppermost part of a plant or the branches.
A plant that definitely needs some help is Heaths black rose, my first one got lots of topping being used for cuts, she will suffer for this as the branches get thinner each time you top so less able to support a big bud but using LST the next time meant the transport system of the plant will not become narrower like topping and fimming and will benefit from the thickness increases of the tied down branches.
In starting LST you tie the main stem down but before you do this you must attach the stem to the other side of the pot for stability and so the roots arent tugged at by the next ties.
You can go right round pot, the main stem recovers quickly and shoots back up, this is when i tie her down again.
Side branching now higher than main stem so most auxins directed to them.
And the finished plant looked like this and yielded much much more than it would left to its own devices.
Dont be scared this technique will always strengthen plants, its a bit like body building the main stem, and if you spend enough time doing it and get round to branches as well you will yield more. This can also be a very good technique for keeping plants low but as I have plenty of headroom I always release my plants in flower.
And heres an example of a members LST
Renegade4-20, brilliant job, plant kept small for a CFL grow