best method to make a nether portal?

the thing that catches you later is linking. a block in the nether is 8 in the overworld, so a second portal built a long way out can link to the wrong one. note your overworld x and z, divide both by 8, and build the nether side at those coords. saves a lot of walking in circles. take a flint and steel through with you every time as well. a ghast fireball can put the nether side out, and without something to relight it you're stuck over there until you find another way home. a lot of people also box the nether end in with cobble for the same reason, ghasts can't do much to it.

no diamond pickaxe yet? do the bucket method. make the frame mould out of any cheap block, pour lava where the obsidian should go and douse each bit with water, it turns to obsidian in place. you only need 10 because the four corners are optional, frame is 4 wide by 5 tall. light the inside with flint and steel.