Lets assume you have safestrap installed already.
Steps;
1. You're gunna need a file manager, such as Androzip, or Es file manager. Both accessible from play store.
2, open file manager and get acclimated to its purpose/use. Create a folder name it A.
3. Download your Rom of choice. This will go into your download folder on sd card. Copy said Rom into folder A. This A folder should be in the same section as all the other folders on sd card such as the download folder, so just scroll up, or down to find it.
4. Boot into Safestrap make a backup of current phone.
5. Wipe cache, user data, wipe everything but sd card(idk if thats an option,lol).
6. Select flash rom.
A screen should pop up with find zip file, toggle signature verify, script asserts..
Hit signature verify, and script asserts.
Then hit find zip file, go into folder A find Rom you put there. Select Rom. Flash away.
7. Hit the thanks button on every post of mine you see! Then your done.
To everybody if anything is wrong, or not added please note.
Hope this helps.