- The Filling
Consideration has to be taken into account on moisture content, size/thickness of the pieces and whether they need prior cooking and/or draining. All the ingredients should cook at the same time, or not require cooking.
- The Wrapper (and wrapping)
Presuming the wrapper is the defrosted conventional Chinese wrapper (flour, water, oil) specifically made for Spring Rolls. Make sure you roll it tight and firm (a loose roll will allow oil to flood in, and seal the final end with ideally a flour paste, but egg wash would work.
- Batter (or no batter)?
Depending on your desired look of your Spring Roll, and when you will serve them (ie immediately after frying, or later as in party or reheat before serving) will help you decide about Batter. Non battered spring rolls don't reheat well, especially in the fryer.
The type of oil, quantity and the temperature of the oil is important.
You need a high smoking/burning point and enough volume of oil to keep the temperature from dropping as you add your spring roll/s.
The temperature will depend on the size (length and thickness) and whether the filling needs to be cooked.
Your spring roll/s should sizzle as they enter the oil and bubble away.
Don't overload your fryer, your spring rolls will start soaking up the oil and possibly start to unravel.
You might also want to check your fryer, a deeper pan would be better then a shallow pan - spring rolls are usually heavy at the start and sink down.
When they float or when they stop bubbling much is a sign they are done.
Depending if you had wet ingredients you might need to make a small prick in two ends and stack them on their ends to drain any excess oil or liquid.
Also your spring rolls should be spaced out from each other as they drain, this reduces them absorbing moisture from each other.
Hopefully yours turns out better!