I prefer an old type wire-stretcher similar to the one in the link below. I don't know about this model in particular, but the one I use often is an old and sturdy model that we have had for a long time. It works great for either stretching and reattaching a broken line or stretching an initial line on a corner post. And I do everything by myself, so I have found that this is easiest type for me to use. There are probably a ton of youtube videos. With any stretching, just make sure you are looking down whole line when stretching to make sure the wire is clear of any snags and make sure nobody is near wire as it is possible to stretch too much and break the line. With these models, also make sure hand is clear of ratchets when you release tension so you don't smash your fingers---Because it hurts like hell.
StretcherEdit: I prefer to use wire to secure t-posts rather than those stupid clips because those break over time. I secure with wire and make sure pointed end of wire is facing out so cows cant get snagged on it.
Best advice I can give you is to run at least one line of high tensile to keep your livestock off the fence line You will save a lot of money in time and repair costs down the road if you use high tensile. Otherwise- your cows will be rubbing all over it if they get lice and don't forget "the grass is always greener on the other side" so they will have their heads through the wire- especially the calves.