It depends on what island you are talking about.
Moonglow is an island...get there via public moongate. Same for Jhelom/Bucs Den.
You CAN get to Serpent Hold isle right from downtown Brit...that red moongate right in town by Lord Brit's will pop you to Serpent Hold. There is a moongate FROM Serpent Hold in the north top most building *nw* in town takes u back to Brit.
Ocllo ...ya need to gate there your self. I got my magery to a little over 50.0 when I first got here and began using runebooks others had made to go mark myself at Ocllo where I still primarily go to bank that and Serp. Hold. Magincia was destroyed sooooo that is a mess at the moment still, boat atm is only way there. Nujel boat or gate !
You can get to *Marble Island* by running up thru the lost lands and entering Marble Isle via the portal in the cave there n. nw nearly to the top of the lost lands ya can do that on foot. . just run gingerly !
You can get to old world original land *portal isle via.. the lost land spot..etc.
Your best bet is to get a mage wand -29 then get yourself some magery scrolls OVER your magery skill...hold the wand...you will try to cast off that scroll you will fail won't matter magery RISES reg free...keep at it..cast off of scrolls for 4th then when those are cast ie your skill increased ...hold wand more..cast 5th fizzle fizzle...keep at it ...then go up to 6th off the scrolls while holding wand ..fizzle fizzle fail wont matter ...remove mage wand after x amt of hours in one short evening you be smarter int. and higher magery ...then go buy gate scrolls and gate to every island you wish to go to...off of rune books in others rune libraries ...........end up going everywhere, just like I do.
Get the magery up...buy some gate scrolls mark from rune books in others rune libraries here or mark if someone takes ya...up magery more wont need the gate scrolls even no more to go anywhere.
I began with 0.0 magery here ! I can res the dead now at 115 if they not factioners and if game mechanics permits ...or hit any island I dream to go visit. . and it all began with -29 mage wand NO regs...and upping my magery till I could gate with gate scrolls ..till magery became higher to never need a gate scroll again. Keep at it..............whole world out there to see ya do not even need a boat !