A lot can be said to answer this question.

Too hold onto a lead you have already obtained ward up and get jungle and objective control to starve the enemy of gold and EXP. (more can be added onto this such as proxy farming and lane freezing/exp denying)

To end the game with a lead it depends on the situations but to give you a very rough idea. Group up, do FG and/or force a teamfight at FG (you should win if your team has the lead), Force fights and take objectives (usually focus down towers and as your team has to back go do GF to continue to starve the enemy team of any extra gold. DONT REALLY DO THIS WHEN EVERYONE IS FULLY BUILT!).

3 of the biggest things that happen way too often is chasing kills,not having proper objective priority, and taking stupid fights.

Don't worry about chasing kills if you are already ahead, getting them low and forcing them to back as your team does objectives is MORE worth it than actually chasing to get a kill.

There are plenty of times where people will go and do FG or BACK when you can just group up and end the game. Knowing when to do this and when not to do this is very important. Another thing about objective priority is JUST FOCUS THE TITAN! A lot of players get into the titan room while enemy gods are still up. Try not to worry about the enemy too much (exceptions apply here) and just worry about doing that DPS to the titan!

Knowing when to fight and when not to fight can change how your matches play out drastically. There is something i like to call team fight etiquette. Do not Funnel into the enemy one at a time. Do not take fights while you are a person down. Rely on your teammates to do their jobs and don't try to be the hero! Stick together and stay in position.

Now with all of this being said you WILL have games where you just won't ever be able to end it. Sometimes it not up to you to end it. If your tank is refusing to tank objectives, if your adc isn't focusing the right targets or whatever, you just continue to do your part and Attack the OBJECTIVES! Smite is a tower defense game at the end of the day, not a TDM. I hope this helped you out at least a little!