there are top post clamps called marine terminals you can buy at napa. they clamp onto the top post terminals of the battery and have a stud that protrudes upward from there. they come in 5/16 bolt thread or 3/8 bolt thread. the cables will bolt onto the studs. get the brass ones if you can find them. make sure the battery posts are clean and straight. I have seen some that were cleaned with a brush style of post cleaner, and they were nice and shiny but they were not straight, so the post doesn't contact the whole terminal because there are voids where the two parts don't actually touch due to a low spot on the post. maybe from a bad connection there previously that overheated and distorted the post or maybe from corrosion. I now use the tapered reamer style of post cleaner that sort of shaves the post down till it is actually straight and clean and shiny from top to bottom.install the marine terminals, then the cable gets a crimped and soldered eyelet style connector that will bolt on to the battery terminal marine clamp. you can use some shrink tube here to cover the bulk of the connector and onto the cable to seal that atrea. shrink tube comes in seberal styles so ask for the stuff with the glue inside. it will heat up and sqyuish out to help seal the connection. they come in red or black (or whatever colour) and will help to keep the cable designation (pos or neg) for future reference. it works pretty well, just also make sure that the other end of the cable is connected well too. the battery negative cable connection is one that gets skipped alot because people tend to write off the ground as unimportant, but if you think about it, it is just as important as the positive side. the power flow can't happen properly if either side is compromised. make sure there is a good ground on the engine and also the frame and the body. from the actual ring connector to a good clean bare metal surface with a star washer under it. then you can paint it with some primer or whatever to keep the elements sealed out. the same goes for the positive side. right from the battery to the starter and alternator, all the way to the fuse box or relay centre or however your configuration is set up. also, if the cables are older, check inside the insulation for corrosion that can work it's way down inside and compromise the conductivity of the cable. I have seen cables with the bolt on connectors that were corroded, so i took the clamp off and was about to cut the cable back some and install the new ring terminals only to find that every time i cut off a piece of cable to start fresh, there was corrosion down inside the insulation. on some that I replaced the other day the corrosion ran pretty much the full length of the cable. no wonder the dude was having starting issues. the marine terminals work pretty well for vehicles that have the big sound systems installed and take power to run the system right from the battery connetion. sometimes these areas can get pretty cluttered and have some "interesting" connection styles to connect enough cables to run all the extra stuff guys need.
if you get the battery cables all good and you still have starter issues, but it will start with a boost, get the starter checked. maybe the starter draw is excessive and a new starter is in order. you can also do a voltage drop test from the battery to the starter to see if there is an issue with conductivity of the cables or grounds.
just a thought.