Ah me matey glad to see you have come to learn the fine art of reaping very good. But the skills, techniques and tatics are as vast as the sea.
I'm a lvl 75 reaper solo slooper myself and use a vast array of tools depending on the situation so i can't say any one particular is the best. Howerver my personal favorite is the fire boat tactic. Which i'll get more into later.
Frist to be a good solo reaper you will need to have a mastery of the basics of solo slooping. Using technique like anchor fodder and such will be of great importance.
Now for some advice.
For these tips the Rowboat and storage creates are your best freinds. Find the and hold on to them they are the most valuable tool to you. More then your own ship.
For PvE:
Skull forts and Burning Blade will be your priorites.
Why?
Skull forts allow you to gain a large amount of loot and rep with little to no risk. Allow me to explain. Frist don't start by putting up the reaper Flag instead sail around till you get a rowboat then park your ship an island over or inbetween some rocks close to the fort. Then rowboat to the fort and kill the boss but DON'T open the vualt. Once you do stock the rowboat with supplies and then take the key on the rowboat. Now you can row back to the ship and then go to an outpost raise the reaper flag and go back to collect the loot quickly. If there to many other ships hold to the key and simply wait for another active fort. This will also allow to obtain a strong hold keg that can be used for both def and off. Don't sell that.
Burning Blade: This is great for stocking the ship as well a practicing your ship combat. You can do the island stratgy as well as ith takes the loot a long time to despawn. It's a bit more risker but your priority should be getting the ghost cannoball create the waith shots make you extremly deadly to any ship.
For quick and safe rep you can do Merchant Cargo Runs. Now before you could sell cargo to the reapers to gain emmisarry rep but this has been recently patched but you can still gain rep by turning cargo to there rightful recipients. Dumb i know but it works.
PvP:
This is were your skills will shine. Earlier i mentioned the fire boat tatic. This is simply taking a rowboat with a keg. I think you can see where i'm going with this. It use to be done with the sloop itself by placing the keg at the front of the ship then ramming into the target then detinating the kegs. It has evolved alot since. Many slight varitations of this but you get the point. Ofcourse this works best with a mega keg from the fort and is best at sinking brigs. Just make sure to detonate the top deck in the middle or front of the boat.
Camping Reaper hideout itself a very common and obviuos strat don't have to explian much.
And finally baitting enermy ships. I can do about 3 pargaph on this so ill stop right here.
In short stealth and cunning are the skills you must master to become a solo reaper as speed and decisiveness are your biggest advantage.