Hi Vizz, please do not clean camera lenses with a lens pen. You will definitely scratch the delicate coating very easily.
1) Get a rubber blower (get a proper sized blower) to blow away all the dust & loose dirt that is sticking to the lens element. If it looks clean enough let it be.
2) If the lens is still dirty & needs a wet clean proceed below with caution.
3) Purchase optical grade alcohol or IPA ( rubbing alcohol from pharmacies or alcohol that is sold by hardware shops have impurities & adulterated with perfume). Optical grade alcohol can be purchased from major photography stores at downtown.
4) Lens tissue.
5) Find a well lighted & minimal dust area to work.
6) Wash your hands with soap.
7) Blow away any loose dirt from the lens element.
8) Remove a clean sheet of lens tissue from its packing.
9) Fold it to a manageable size, do not touch the area of the tissue which you'll be using to clean the lens element.
10) Drop a few drops ( 2-3 drops) of cleaning fluid on the tissue, too much cleaning fluid & the tissue will be too wet & it'll leave cleaning fluid stains on the lens element.
11) Hold the tissue at an angle & gently place it on the center of the element.
12) Apply gentle pressure on the tissue & in a slow circular motion, wipe from the center of the element to the edge of the element. While you are wiping observe that the cleaning fluid is drying from the lens element just as the tissue moves away. If you wipe too fast or too slow, it'll leave cleaning fluid marks on the lens element.
12.1) Use the lens tissue for only one cleaning job, discard the used tissue. Use a new piece of lens tissue every time if you need to redo the wet cleaning again.
13) If you are inexperienced, please practice on cheap coated filters. Check the filters for scratches after you have cleaned them.