Soldering 259 plugs is easy.
i use a 100 watt soldering iron with very large copper tip, which is needed to get as much heat as quick as possible on the spot.
Most mistakes are a too low wattage soldering iron, or one with a small tip.
Clean your stuff, i use a file to clean the holes in the PL259's and tin them in advance.
Be very secure in cutting the coax to size see several instuctions on the net.
Pre tin center conductor of coax, use file to remove excess if needed., thinly.
Mount coax in plug, using the big copper tip it is a question of seconds to get the braid thinned with the connector, once the solder has flowed, wait a few seconds, cool off plug with dampcloth, solder center conductor, done.
I keep that old trusty 100 watt soldering iron just for that since 30+ years, never failed.
Even doing aircom plus aircore insulated coax for 2/70 which melts even faster as full polyethylene RG213 etc.
The game is to get as much as heat possible as fast as you can to the braid and connector for a reliable solder connection and after setting, cool off a.s.a.p.
That way the isolation cannot melt, the center conductor wil stay in it's place and you won't get an impedance bump.
as soon the center conductor gets out of it's place in respect to the outer copper layer you have an impedance bump there, which you won't like.
Do it right, and an good connection is worth the effort.
Specially running expensive radio's or amplifiers.
You want a good connection there before blowing anything expensive up....
Though my ham radio is protected for it, my Heathkit SB-1000 would not like a bad connector..
P.S. use only the best connectors money can buy, not the chinese junk.
Mine are the old silvered ones, i have a lot of them spare, good quality pays off.
Not sensible to spend big bucks on expensive low loss coax to screw it up with el cheapo connectors is it...
One reason on 2 meters and up i only use N connectors, pressure fit, no soldering needed, but the cost 15 bucks a piece......