Partnership airlines that are formed by the alliancing of airlines of some countries together, for instance, Oneworld Alliance (created by British Airways, American Airlines, Qantas, and Cathay Pacific) and Sky Team (comprised of Aero Mexico, Delta, Air France, and Korean Air) are providing excellent services to Plan a round-the-world trip with cheap flights & hotels
To book an economical plane ticket, what you have to do is to your search on sites, compare the deals provided by all the airlines available and select a suitable one according to your budget. Make sure to try to pick an airline with low-cost flights because only the visitation of each country is going to be much expensive, and some cities are much costlier than others.
After you are done with these bookings of flying. Think about transportation, food, and especially clothing because there will not always be summer that you can be traveling freely with just a little luggage. Last but not least, decide whether you are going solo or accompanied by the family and construct your planning according to that.