The only method that can reduce the risk of spreading or contracting STDs/STIs and unwanted pregnancy is a condom (external and female) if used consistently and correctly. Using a water-based lubricant is A-OK, but don't use anything with oils in it because it can make the condom ineffective. Something called "dual protection" (using condoms and a more effective birth control method at the same time) may be the very best approach. It is important to know that there are some STDs, like herpes and HPV that condoms are less effective at preventing.
In the U.S. young adults and teens have high rates of STDs. Hormonal birth control methods do not prevent STDs or HIV nor are they 100% effective for preventing pregnancy. Using a latex lubricated condom every time is a smart choice when it comes to protection against both STDs and pregnancy.