While the humble hand job is often eschewed in favour of oral or penetrative sex, there's no reason it can't be just as satisfying. Whether you're looking for a safe way to play in the early days of the relationship, a way to pleasure him when you're not in the mood or a great form of foreplay that will also teach you about his body, using your hands on your man should not be underestimated.
Lube can make things flow so much more smoothly: it reduces friction, helping your hand glide more easily, and opening up a whole host of techniques.
Apply the lube to your hands to warm it first - warming and tingling lubes can help add an extra thrill - then stroke your man from the base of the shaft to the tip of the glans. Listen to his body as well as his groans - if he arches towards you, chances are you're hitting the spot. The frenulum (the string that runs from the glans to the shaft) can be particularly sensitive, and letting your thumb glide over it with every stroke can offer a particularly delicious tease.
Don't just use one hand: let the other explore his erogenous zones. Some men enjoy ball play: try softly stroking them, cupping them or gently tugging on them as you stroke his shaft. And if he's into prostate stimulation, try combining that with masturbating his shaft.
Alternatively, use both hands on his shaft. Trying lacing your fingers together (making sure to lube your palms first) then sliding them over him, pulsing your palms as you go. Alternatively, use one hand to stroke up and down his shaft while the other one cups the head of the penis, circling (in a move sexpert Lou Paget calls 'Squeezing the Orange') If he's well endowed, you can also use one hand on top of the other to snugly enclose his member.
Don't just use one hand: let the other explore his erogenous zones.
Best of all, learn from the man himself. Ask your lover to masturbate in front of you, putting your hand on top of his to feel how tightly he grips, how fast he moves and where he positions his fingers. You can guarantee he'll have a lot more practice than you and will know exactly how to best pleasure himself. Copy his moves and you won't go far wrong.