take it into a tackle store with a line spooling machine, best way imo and the only way

agree with matt ... if your not sure of what your doing take it to someone ...

but if you realy want to give it a go i wrap a piece of electrical tape onto the spool to give the braid something to "bite into" from the start .. then when tying the line to the spool make sure it loops the centre at least 3 times before you tie the knot then tighten very hard. the hard part is then getting the braid on as tighgt as possible (some ppl wet it too but i dont) when i say tight i really do mean tight .. most of the plastic spools ive used are melted on the edges because of the friction needed to get it on as tight as possible for the strenth of the line. 

only other way is fill it up as best you can - plus a bit, then once out in the boat run most of it out(not all bit until you can see the backing) then wind it back in under 5 knots pressure - guarantee that will be tight. This is what Nomad make all clients do before chasing GT's so I guess it is pretty good as a method. I do this on popping and trolling gear each year when I go up north just to make sure.

Best to wind a few metres of mono (masking tape does work too as suggested) on the spool first and tie the braid to this (double uni knot).  Nothing worse than getting a decent fish and having the line turn and run out off the spool and you can't do anything to stop it. 

Tackle shop with a winding machine is the easiest way to spool up - I have spooled a few reels at home running the braid through an old tea towel (so it doesn't cut the crap out of your fingers) to get it nice and tight.  If you have another person handy get them to put pressure on the spool with a tea towel or rag on each side.

Cheers Paul

Ive spooled it onto an old reel first, then from that onto the reel i want it on using the drag to apply a bit of pressure.

Running it out behind the boat while underway, with just a swivel also works well. 

But never again with expensive braid. I am ALWAYS going to take the reel into the shop and have them spool it for me.

Thanks everyone will try the best I can

In a pinch, if you have someone to help you, you can have them hold the spool on some sort of spindle (like a screwdriver or bolt) and then jam something up against it on one side to control the pressure. I've got two little conical wood blocks with holes through them I cut out of some scrap wood. If you do it right and use nylock nuts, you can place the bolt a vice and no extra person needed. I still prefer getting a tackleshop to do it, but sometimes its 9pm and you're heading out at 6am with not many options.

For light lines, my trick is to get a length of mono, tie it in a loop, pass the loop through the spool and put a brick on either side then move the bricks apart to give it some tension/resistance. Put the reel on a rod so you can keep the pressure on by keeping the rod a little bent.