When you get your blood pressure taken systolic blood pressure is the higher number and diastolic blood pressure is the lower number. Two other measurements can be taken from systolic and diastolic blood pressure: mean arterial pressure is one third systolic plus two thirds diastolic; and pulse pressure is systolic minus diastolic.
Cardiac output (which is equalled to heart rate multiplied by stroke volume (stroke volume is affected by blood volume)), arterial width/peripheral resistance and arterial stiffness are some main factors that could affect blood pressure.
Salt reduces blood pressure, but not much or in amounts that would suggest that high salt diet causes hypertension or low salt would reverse it. Restricting salt increases activation of the renin-angiotensin-aldosterone system (RAAS) and noradrenaline, which has some undesirable effects such as increasing insulin resistance and oxidative stress.
Obesity, insulin resistance, endothelial dysfunction, atherosclerosis and poor kidney function are some of the mechanisms of hypertension and tend to affect blood pressure by increasing the activity of the sympathetic nervous system (SNS), the renin-angiotensin-aldosterone system and arterial stiffness.
Some Strategies for Hypertension
This is for informational purposes only and is not meant to diagnose or treat any medical condition.
Obesity, even without insulin resistance, is one of the major factors in hypertension. See Obesity
Insulin Resistance and Type 2 Diabetes
It’s estimated that 50% of people with hypertension are insulin resistant . Insulin resistance increases SNS and RAAS activity and impairs endothelial function, and type 2 diabetes is the major cause of kidney failure . See What Causes Insulin Resistance? Part VII
Endothelial dysfunction and atherosclerosis can increase arterial stiffness and blood pressure (particularly systolic). See Cardiovascular Disease
Psychological stress/anxiety can definitely increase blood pressure in the short term and is a factor in white coat hypertension, but it’s debatable as to whether it causes hypertension. That being said, meditation reduces blood pressure in people with mild hypertension 
Reducing salt does reduce blood pressure, but not by much, although more so in people with hypertension, poor kidney function and African Americans. Don’t expect that reducing salt will normalise your blood pressure. Most sources of salt are in processed foods, take-away foods, restaurants and added salt. Whole foods are usually very low in salt*
Potassium supplementation may be more effective than sodium at reducing blood pressure. However, it also has a fairly minor effect and seems to only be effective in those with hypertension. Potassium also doesn’t seem to increase SNS and RAAS activity like salt restriction does . Although another meta-analysis found no benefit 
Sun exposure is associated with lower blood pressure . Vitamin D inhibits the RAAS , but supplementing vitamin D may not as sunlight increases nitric oxide 
Vitamin K2 may be helpful as it prevents calcification of arteries