I have a technique for making breast forms that are easy and inexpensive. What I do is buy a four-pack of playdough. I mash 2 cups of dough together into a ball and put it into a ziplock bag, squeezing all of the air out before zipping it closed. Then I place the bag inside a single leg of an old pair of pantyhose. I then twist and wrap the hose back and forth over the dough ball until I've all the hose. (the video makes this clear). I make a second one the same way. The playdough can then be shaped into whatever form would complement the particular outfit your are wearing. They can also be molded into a D shape and used as a push-up to show some actual flesh as false boobage. They usually stay pliable for a few months before getting too hard and needing to be replaced.
I used this type of breastform for years before getting silicon ones. I use the silicon most of the time these days but still occasionally find the playdough ones work better. In April 2013 I wore a tight black dress in Las Vegas and the silicon breastforms were too big and were visible in the neckline and on the sides. Luckily I had brought my home make forms and they were perfect.
I've tried several things and sometimes combos of them. I sometimes use tape to create a little extra cleavage or fullness. To do this you stick the end of about a 20 inch piece of tape under your arm pit, then under one breast, then up the far side of the other. Then do the same from the other side to squeeze the chest flesh together. It works ok but movement can be restricted, the tape can be unsightly in certain clothes and the tape will slowly lose its grip.
I've also tried commercial chest enhancing bra-like straps that are tight and fit below the breast level and can push the flesh up but I just don't have enough flesh to push up.
So mostly I use a combo of breast forms and shading. I use smaller forms inside a tight bra and tuck them off to the sides under the flesh so that they act like push-ups. I use brownish blush and eye shadow to make an arc around the breast. The best way to do this is to place the heel of your palm on your nipple and rotate your hand up and out like a windshield wiper. Right hand does the right side and left hand does the left side. (not at the same time unless you are really talented). The shading should be lighter and more diffuse towards the top and darker and narrower as it approaches the cleavage area so that it eventually becomes almost a line at the bottom. I also use white eye shadow to highlight the part of the breast that I want to stick out.
The push-up works well in when out in public however anything but the subtlest shading is obvious in real life. Dramatic shading is best for photo sessions.