Use the entire acceleration lane
The on-ramp ends in a long straight section called the acceleration lane. Its job is to let you reach highway speed before you merge. Use all of it. Match the speed of the traffic in the lane you intend to enter — usually within 5 mph of it — before you merge.
Signal, mirrors, blind spot
About halfway down the acceleration lane, signal left. Check your left mirror and then turn your head to clear the blind spot. Pick a gap and steer smoothly into it. Don't slow down to find a gap; speed up or coast and let one open.
What never to do
Never stop on an on-ramp. A stopped car merging into 70 mph traffic is the leading cause of catastrophic merge crashes. Never use the shoulder as a merge lane after the acceleration lane ends. Never expect highway traffic to move over for you — sometimes they will, but you cannot count on it.
Right after the merge
Once you are in the right-most lane, ease off the gas slightly to settle into the flow. Move one lane left only if you need to and only after a full mirror and blind-spot check. The right lane near an exit is fine for a few seconds; staying in it across multiple exits is not.