Some stillers simply just save the hearts cut for drinking, and recycle all the feints back into the next run, or into the feints jar for an all feints run when it is full. Some like to blend small amounts of various fractions from the heads and/or tails back into the hearts, to add particular flavors. There is no right or wrong way. Personal preference rules here, determined by experience.
Being capable of cutting the fractions directly off the still and without a alcoholmeter/alcometer etc is a huge accomplishment for a distiller. But for the novice, this is a daunting art that will take runs (and mistakes) to perfect. There is an easier way, however.
Procure a good number of small (say 500ml) jars, number them, and get a big ol pot that is big enough to hold everything you'll want to blend. Collect your run in these numbered jars, and leave them to air out for a day or two with a coffee filter or similar cover over them to keep out bugs and dust. Some of the more volatile and unwanted components will evaporate off over this time, and you'll be able to make better cuts and blends.
Now, when the time comes to makes cuts, or do any further blending, you have to remember that the spirit will smell and taste different when watered down. The tails in particular seem to come out with dilution. To get around this, when tasting for blending, dilute a small sample with some very clean water in a clean glass, swirl around and mix well. Aim for a %ABV of between 35-40%. Then have a gentle sniff of each, do it 2-3 times, with all the fractions.
Then try tasting them in very small amounts. Don't swallow the product, spit it out. Seriously!!! Making cuts/blends when drunk usually leads to a substandard product and many regrets. Rinse your mouth with water between tastings of the different fractions.
First make the main cuts between heads-hearts, and hearts-tails. For the novice stiller, it is probably best to just learn this first, before moving onto the more complicated and tricky art of blending.
If you want to blend some of the other fractions in, start with the cleanest section of hearts, and work up and down the line, adding heads and tails into your blending pot one by one. Only add very small amounts at a time. If in doubt, be conservative and blend a small amount first in a trial glass, then you haven't made an awful mistake if it doesn't taste good. Depending on your tastes and the recipe, you can expect to keep around 30 to 50% of the total volume collected in the blended product, and the rest will be feints.
If you mess up the cuts or blending, for whatever reason, you can just throw it all back into the still, minus the foreshots, then add some water to dilute it a bit (or the backset from the run), and run it all over again. It is a good learning experience.
After you have finished your blend, everything remaining can be treated as feints and reused or stored for an all feints run.
The first time you make cuts, and especially blends, it will probably be quite difficult to pick the often subtle but important differences in smells and tastes, and you may not be happy with the result. But do not be discouraged, this skill improves a lot with practice, and in many ways it is the most important skill of all for a stiller to develop. So be patient, and just keep practicing!