The problem with this question is that static friction and kinetic friction are not fundamental forces in any way-- they're purely phenomenological names used to explain observed behavior. "Static friction" is a term we use to describe the observed fact that it usually takes more force to set an object into motion than it takes to keep it moving once you've got it started.
So, with that in mind, ask yourself how you could measure the relative sizes of static and kinetic friction. If the coefficient of static friction is greater than the coefficient of kinetic friction, this is an easy thing to do: once you overcome the static friction, the frictional force drops. So, you pull on an object with a force sensor, and measure the maximum force required before it gets moving, then once it's in motion, the frictional force decreases, and you measure how much force you need to apply to maintain a constant velocity.
What would it mean to have kinetic friction be greater than static friction? Well, it would mean that the force required to keep an object in motion would be greater than the force required to start it in motion. Which would require the force to go up at the instant the object started moving. But that doesn't make any sense, experimentally-- what you would see in that case is just that the force would increase up to the level required to keep the object in motion, as if the coefficients of static and kinetic friction were exactly equal.
So, common sense tells us that the coefficient of static friction can never be less than the coefficient of kinetic friction. Having greater kinetic than static friction just doesn't make any sense in terms of the phenomena being described.
(As an aside, the static/kinetic coefficient model is actually pretty lousy. It works as a way to set up problems forcing students to deal with the vector nature of forces, and allows some simple qualitative explanations of observed phenomena, but if you have ever tried to devise a lab doing quantitative measurements of friction, it's a mess.)
In your graph you have only plotted kinetic friction as a function of time and by the formula
$$F_k=\mu_kN$$
it remains constant because it is independent on the force(horizontal) you apply, surface area, time etc. however if you also include static friction in your graph it would have looked more like this:
Source: http://deutsch.physics.ucsc.edu/6A/book/forces/node21.html
From graph we can see:
Kinetic friction - remains constant
Static friction - increases and is equal to the force applied to remain in equilibrium until applied force is smaller than:
$$F_s=\mu_sN$$
based on experimental observation it almost always turns out that static coefficient of friction is greater than kinetic coefficient of friction
$$\mu_s>\mu_k$$
Therefore the maximum force that we can apply on an object so that it can remain in equilibrium is greater than the force of kinetic friction which is constant, because of this we can observe that force of friction is decreasing when the object starts moving which is seen in the graph above colored in green.
Best Answer
In general, smoothing the surface, changing the interaction from sliding to rolling, adding (air) space between the surfaces, and adding lubrication (oil, graphite, teflon, ball bearings, air cushion...) are the most common techniques.