Your skin will become thicker and more oily as your pores largen and oil production increases
 

The smell of your sweat and urine may change. Typically your sweat becomes 'muskier' smelling.
 

Fat deposits in certain parts of your body will begin to redistribute. Typically, fat in your thighs and butt will shift toward your abdomen (stomach). This can help you look less curvy, though your bone structure will not change, with some rare exceptions.
 

Your breasts may shrink a little and become a bit saggy. This is due to the lower amount of estrogen in the area. 
 

Gaining muscle will become easier! With the right diet and exercise, many trans guys taking testosterone find their legs and arms have more muscle definition, often with more prominent veins and a slightly rougher appearance. 
 

Your eyes and face may begin to change shape as fat redistributes. Many trans guys taking testosterone experience "tom cat-ification" where their cheeks become very round for a while as their body adapts to the initial changes.
 

Your vocal chords will begin to thicken and your voice will begin to drop, akin to how cisgender boys' voices drop during puberty. Your voice early on testosterone may sound squeaky or similar to a vocal fry, but voice training can slowly fix this. Issues of vocal fry may resolve itself on its own after taking testosterone for many years. Your voice will begin to drop within a few weeks of starting testosterone and will not reach full maturity for at least 5 years.
 

Body hair will become more prominent. Hair on your chest, back, and arms will increase in thickness and will become darker. It will also grow at a quicker rate than before. You MAY develop male pattern baldness if other cisgender men in your family also have the condition. Unfortunately, male pattern baldness is not curable, but can be treated with topical medications such as finasteride, minoxidil, etc. Even if you do not experience male pattern baldness, hair thinning on the front of your scalp is relatively common.
 

You may begin growing facial hair. This result varies heavily from person to person and each person's facial hair will have different degrees of thickness and coverage. Starting testosterone later in life (40 and above) may result in less overall facial hair growth than those who start at younger ages. Using hair growth treatments like minoxidil may promote the growth of facial hair, though be warned that minoxidil is extremely toxic to household pets!
 

There may be vaginal dryness and partial atrophy of the vaginal walls. Not everyone experiences dryness to the same degree. It can be temporarily treated with a water-based lubricant, or treated long-term with a topical estrogen cream - don't worry, the cream isn't strong enough to 'undo' the effects of testosterone.
 

Eventually, you may see menstruation slow and/or eventually totally cease. If you experience spotting/bleeding randomly after not experiencing it for a while, talk to your doctor. Some trans guys taking testosterone may not experience a cessation of menses at all. Ironically, an excess of testosterone may return your periods, so it is important to keep to your prescribed dosage.
 

After a short time, your clitoris will begin to lengthen and widen. It will also increase in sensitivity. Many people experience uncomfortable chafing against their underwear as the clitoris grows (often referred to as "bottom growth"). Most trans guys taking testosterone will average 1 to 2 inches of erection after growth slows. The size of your growing clitoris depends on genetics. Some 'pump' their clitorises in an effort to increase their size, though it is not confirmed that will make a long-term difference.